technology has been around for centuries. It started out with advancements in medicine, especially the discovery of antibiotics, and has since advanced greatly.
The majority of lethal diseases have since been eradicated, and while natural human lifespans never exceeded 200 years, the various forms of life extension available for nearly a millennium allow for theoretical lifespans of thousands of years and possibly longer.
Depending on the polity, life extension isn't necessarily available to everyone to the same extent. At the same time, not everyone with access wants to greatly extend their lifespan, or agrees with the available methods.
A number of technologies, including gene therapy, stem cell treatments, and nanomedicine are able to extend a person's lifespan significantly by reducing the amount of permanent damage sustained from everyday life.
While it's still not possible to completely undo that damage, slowing down the natural aging process to near zero for decades is entirely achievable. As a result, people well past their hundreds will appear only a decade or so older than when they started the treatment.
Most people start the process somewhere between age 25 to 35, allowing them to retain a youthful adult appearance the longest. Some cultures favor an older appearance, and thus it's more common for people from those cultures to start life extension treatment a decade or so later.
Personal preference and overall health also play a role in when, and to what extent, life extension is an option.
A radical, and very different, approach is to upload one's mind to a computer. That creates a copy, and it's not unusual especially for cyborgs to upload static copies as mind backups. Some link their digital copy to their biological mind, essentially doubling their mind and keeping a live backup.
It's still a lot less common for people to go entirely digital, destroying their biological body once the upload it complete. Most who go that far do keep an android body around to make interactions with their biological kin easier.
Uploading is the most expensive method, and still somewhat experimental.
have mastered life extension. While not immune to injury and the effects of cosmic entropy, their natural lifespan is as close to eternity as physically possible.
Many of the important figures in the JNF
have been around for hundreds of billions of years, and show no apparent signs of old age.