Delimiting

When a child's magical ability begins to outstrip their decision making ability (usually around the age of 3 - 4) by advancing beyond the usual simple creation of lights or sounds, the child is taken to be fitted for a Limiter. Limiters can take many forms, but generally consist of a gemstone (even quartz will do, so these are rarely expensive) and some method of attaching it to the child. Limiters can be earrings, bracelets, or even necklaces. The idea is that it be something the child cannot easily remove themselves, and which helps to absorb some of their Magic when it flares. 
When a child comes of age, their Limiter is removed in a ceremony called Delimiting, and they gain access to significantly more of their Magic than they had previously enjoyed. Part of the ceremony usually includes a test of magical ability which can help to guide the newly Delimited child to know what they have a natural affinity for, at least at the time.

History

Since the rise of Magic, all humans are born with an affinity for Magic. This changed the way that life was lived across the world. Suddenly, Magic went from something that villagers feared and that kings needed to be aware of the uses for to a fact of life for every new parent. Magic grows with an individual, but it is also very personalized for each person, and is subject to change based on the feelings and intent of the person to which it is attached. This meant that raising children was … complicated... for the first few years. There are few things more frustrating than a toddler telekinetically scattering their breakfast each morning until they get bored of it, and that is on the least dangerous end of the scale.   Luckily, it only took about a decade for Limiters to begin circulating throughout the world. Of course, that didn't help the generation that grew up unLimited, but they found other means of assistance in those early days. In fact, modern detractors of Limiters often cite the original unLimited as the reasons for their own refusal to Limit their children.
The age at which children have been Delimited has gone up over time. When Magic first rose to prominence, children had their Limiters removed and their aptitude tested at the age of seven. The age slowly crawled upwards to nine, then to eleven, and today most children have their Limiters removed at 13.

Execution

The Delimiting is a simple affair. The physical act of removing the Limiter is usually simple. An adult removes the Limiter and tells the subject that they are deemed worthy of their Magic. Usually, their friends and family then bring presents and a meal is had at the expense of the family of the newly Delimited child. At the end of the party, the guest of honor will channel their magical energy into a divinatory medium which helps to show their affinity. 
The results of this divination are required by some governments to be reported by the age of fifteen, which in those countries effectively serves as a hard ceiling to the age of Delimiting.

Components and tools

Although the mediums for magical testing were originally crafted by the child's family, or someone close to the family, today these mediums can be bought in test kits at most drugstores. The traditional test is a series of small figurines, each representing a broad specialization of Magic. The stones are enchanted to spin in response to Magic, and the one that most closely represents the affinity of the figure being tested will often spin very rapidly, or even jump into the air or be thrown across the room. The responses of the other figurines will typically be there but will generally be much less pronounced.

Participants

Of course, the child who is having their Limiter removed is the guest of honor. Usually, the person who removes the Limiter is a parent or guardian, although it is also not uncommon for it to be an older sibling, or even a leader in the community, such as a beloved teacher or priest.