Psychological and Cultural Effects of Long Life Spans

Elves and humans are physiologically very similar except elves live roughly five times longer than humans do. Not only this, but elves stay in their physical prime for a larger percentage of their lives than humans. Some Scarterrans, humans, elves and others have openly wondered why elves are not dominating humans. Elf warriors have five times the time to hone their weapon skills, elf leaders have five times the time to hone their tactical skills. Elf builders should have the expertise to make better fortifications, better tools, and better arms.
History is full of small groups of powerful people dominating larger groups. Dragons are stronger than everyone but it is joked that dragons can barely tolerate each other long enough to mate and raise offspring. Dragons certainly aren't capable of unifying to conquer the world. Elves are hardly perfectly unified, but they are far more united than dragons and they are at least as unified with each other as humans are if not more so. Maybe elves cannot rule the entire world in the the Third Age, but they should at least be able to dominate humans in their local regions but instead elf princes have to treat human princes as equals.

On average, elf warriors are a little bit better than the average human warriors and elf craftsmen are a little better than human craftsmen. But that is average people, and many humans are not average. The best warriors and craftsmen in Scarterra are disproportionately human.
This is counterintuitive to humans. This leads one to wonder if humans have superior minds or that elves have some kind of learning disability. The answer is mostly no, but partly yes. There are multiple factors that explain why elves aren't supermen.

Longer lived races tend to stretch out adolescence

In every mortal race, whether they are long lived or short lived, children and adolescents lack discipline but their minds are primed for learning. Longer lived races such as elves tend to culturally stretch out adolescence longer than physical adolescence.
Most elves consider the age of majority to be about 90 years old. Physically, an elf is done physically maturing sometime in his/her early fifties. Most human societies consider the age of majority at 16, 17, or 18. And a human is usually physically done developing at 15 or 16. Humans don't waste time.
Part of this long adolescence is a product of elves' love of slow time. Even relative to their long life spans, elves remain in their physical prime longer than humans. Elves don't pump out babies nearly as fast as humans, and they tend to subscribe to the idea that "it takes a village to raise a child." A lot of young elves secretly fear adulthood and enjoy not having many responsibilities while having a bunch of adults looking out for them. By contrast, most human children and adolescents say some variation of "I can't wait till I grow up!" often.
Among humans, both lowborn and highborn families put a lot of pressure on their children to marry and produce grandchildren at a fairly young age. Elves, especially low born elves, don't arrange marriages nearly as often as humans do. Though they are physically mature by age fifty, elves commonly discourage young elves from even thinking about marriage and courtship till they have seen at least a century. There is no hurry and both young men and young women are expected to gain some life experience and wisdom before they can figure out whom they should mate with.

"Slow Time"

Elves have moments of slow time and "fast time". In vulgar argot, elves call this "normal time" and "human time". Elves and humans still have 24 hours in the day and sleep for roughly a third of that day. Elves and humans still have 365 days in the years and they have the same cycle of seasons.
To an elf viewpoint, a human lives entirely in "fast time". Elves prefer "slow time" whenever they can. Elves will figuratively and literally stop to smell the flowers. An elf will typically take much longer to eat her meals than a human does because she wants to savor her food while the human is thinking about what she wants to do after dinner. Elves like to savor courtships. Elves like to day dream. Elves take longer when reading because they will stop to ponder specific passages. Most elves are so content with inner reflection and living in the moment that boredom is almost an alien concept to them.
A human carpenter practiced his trade from childhood into adulthood and did less else but think about carpentry. Most other humans would be happy to have a skilled carpenter build their house. All four elf culture tend to value being self sufficient. When possible, they want to build their own houses, cook their own meals, and craft their own tools. This broad approach to things slows down an elf's quest for excellence. Going back to the house example, they will talk to other elves about carpentry first whereas a human is likely to fall back on his own education and trade their services for those of a carpenter.
This can go a long way to explain why an elf that practiced sword fighting for thirty years is on the same level as a human who practiced sword fighting for five years. The elf is in slow time. He didn't train with the same intensity over those thirty years that the human did over his five years. While the two are equal soldier, the elf swordsman is a probably a better cook, a better poet, and a better carpenter than that human swordsman. On a more practical side, the elf is probably a better strategist and archer too.
Elves are not lazy, frivolous or stupid. If there is a house fire, an elf is not going to stare at the intricate shapes of the dancing flames in fascination. He will race to find a bucket of water just as a human would do so. Elves can and do respond to emergencies in a timely manner. They can also keep to a critical schedule. An elf peasant farmer knows just as well as a human farmer that if he doesn't get his planting done in a reasonable period of time, the end of the year harvest will be bad and his family may go hungry.
In other words, when an elf must act quickly and decisively, he or she will act quickly and decisively. This is what elves call "fast time." There are exceptions, but most elves don't want to fall into fast time longer than they have to.
Very few elves will admit it, but they are not as good at handling stress as humans. Lucky elves live just over five centuries. Typical elves live around four centuries. Some elves can handle fast time better than others, but An elf that spends large portions of her life in fast time is probably going to age fast and is likely to succumb to age based illnesses before or shortly after her third century. Elves that spend a large portion of their lives in fast time are at a high level of risk to develop a mental illness and whether or not they have a clinical issue, they are probably going to be somewhat socially off putting from other elves.
On the plus side, an elf that is well accustomed to fast time is going to be a lot more efficient at developing skills and accomplishing tasks than a typical elves. In this case an elf that studied sword play for thirty straight years with the focus of a human is going to be able to fight with the strength of twenty men.
Not just this, an elf that is able to continuously maintain a human like focus could end up mastering many, many skills. You might find a master swordsmen who is also an master alchemist and a master blacksmith and a master historian. Perhaps he researches legendary magical weapons of yore, then figures out how to replicate them and trains extensively so the blade has a worthy user. Even in the Third Age, a disproportionately high number of Scarterra's greatest mages are elves.
Depending on what they do with great abilities, elves like this are simultaneously both pitied and honored, for they have sacrificed their own happiness to develop skills to aid their society. Or maybe they are just out for themselves... These elves are little more than social outcasts but other elves follow their exploits with morbid fascination none the less.
Elf leaders, those born into the leadership position and commoners who earned informal leadership positions tend to adapt quickly to fast time or they find they are stripped of their titles. As a matter of course, leaders have to constantly solve problems as they come up, so this means they don't get to enjoy much slow time. Despite having lots of access to best mundane and magical healers and eating the best food, elf leaders tend to have average lifespans at best.

Undead and other artificially extended life spans

It doesn't matter what mortal race someone was in life, cheating death is not only difficult, but it has a high price that is immediately apparent. Mortal minds can only handle so many memories and experiences without issue.
If a mortal is artificially extending his or her life span with magic, then it's not a question of if the mortal will go mad, but when.
Not only is an undead brain not able to comfortably assimilate, two, ten, or a hundred lifetimes of knowledge and memory, but most undead are separated from the simple joys of life. Even if an undead is not physically harmed by sunlight, it is not going to be able enjoy a warm spring day the way a living person could. Food, drink, company, sex, comfort, laughter...all these things are harder to enjoy the longer a creature remains undead. This makes coping with the long years even harder.
If they are lucky, a free willed undead creature might develop a high functioning form of mental illness, but this is not always the case. A lot of liches and vampires end up committing suicide. Others develop schismatic personalities, especially if they became undead specifically because they were afraid of death. They fear death with a passion, but they also subconsciously hate their existence and secretly want to die. Such tortured souls, rather commit suicide outright they will concoct highly risky schemes for advancement in order to provoke an outsider into killing them.
Most free-willed undead are plotters and schemers by nature. Since they both want to live forever and also harbor a secret death wish, their schemes can seem nonsensical to outside observers as they alternate between absurd levels of caution only to react to a small threat with overwhelming force later.
One of the best ways for an "immortal" undead to retain his/her sanity is to pick a goal that is very difficult to achieve. "If it takes me 10,000 years I swear I'll _______". Of course there is always the danger that they accomplish their elusive end goal, at which point the undead creature is likely to enter a near catatonic state as the rewards of the destination are probably not half as satisfying as the journey.
For good examples of how grand ambitions and madness intersect, one might look at the vampire lords. Vladimir the Conqueror literally tried to conquer the world and ended up goading the world into killing him. Rallark the Loyalist has set the grand goal of destroying every vampire but himself. Lorshellis the Successor waxes hot and cold between wanting to take over the world and wanting to save it. Vralic the Hunter is obsessed with finding an honorable death worthy of his magnificent life and unlife. Dalak the Dark One is now Scarterra's most powerful Infernalist and no one knows exactly what is doing, but Infernalists are all mad and ambitious in a nihilistic way.

Slow time isn't just for elves

This article compares and contrasts elves and humans a lot, but most of these comparisons apply to other races. gnomes and dwarves live substantially longer than humans, among others. Most of the basic principles in this article talking about elves apply to the other long lived mortal races.
Dwarves are not known for stopping to smell the roses or enjoying deep self reflection, but they are not commonly rushed either. When they are working on almost any task, it is more important for them to do it perfectly than for them to do it quickly. About the only time a dwarf rushes a personal task is if lives are literally on the line.
Dwarves also find comfort in repetition.

Dwarf, "Did I tell you about my clan's glorious history?"
Human, "Only about forty times...."
Dwarf "I better make it an even fifty then. It all began when...

Whereas elves acting in slow time tend towards self reflection, dwarves prefer to strengthen their ties of community in some way. This is why dwarves seemingly never get tired of telling the same same histories, the same old stories, and the same old songs over and over again.
This ties into the dwarves' tendancy towards high filial piety and ancestor worship. They can not only name all their ancestors five+ generations back they can tell the stories of their ancestors' victories and defeats.
According to the gnomes' own legends, they were created to build bridges and alliances between dwarves and elves during the Second Age. Thus it is not surprising that a gnome's sensibilities are roughly half-way between those of a dwarf and an elf. Gnomes like to take time to smell the roses and reflect inwardly and they also find comfort in repetition, telling and retelling old familiar stories especially if the repetition reinforces family and communities ties.
Among non-humanoids with long life spans, it is difficult to make generalities. Dragons, kraken, and aranea often fill their time with plotting and scheming. They make brilliant plans and back up plans and back up plans to their backup plans. Delvers and giants just seem okay living life one day at a time.

Mortal Life Expectancy by the numbers

Type

Natural

What about the short lived races?

Humans don't live nearly as long as elves, gnomes, or dwarves. That said, there are some races that don't live as long as humans.
It is theorized that they experience a more extreme version of "fast time" though this is often denied by the other races who say this is a flimsy justification for racial prejudice.
For instance, tengku don't typically live as long as humans. Some say that this is a major contributor of a tengku's avarice. Because they know their own mortality is coming, they want to own everything they can now.
Ojiongo are the shortest lived of the major Scaraquan mortal races, and they are known to be very ambitious and power hungry. They only have a short time to make their mark and this supposedly drives their Byzantine machinations.
Some say a short life span leads orcs to extreme risk taking and a desire for glory, but orcs only age slightly faster than humans, so this supposition is a stretch.
Kalazotz have shorter life spans than most, and they are pretty mellow and patient. Satyrs have fairly long spans and they are notorious hedonists that seem focused on short term concerns. Both of these seemingly disproves the rule that shorter lived races feel pressure to life to the fullest and the longer lived races are more patient.