Meds or no meds is a very individual decision, and maturity or age isn't a key player. Most people who quit, go back on their meds because they don't have the coping skills to deal with the symptoms.

I myself quit my meds due to side effects and the only available pdoc being unwilling to accommodate me because I'm "stable".
But sometimes their stablity comes at too high a price, and that is when I actually advocate trying to taper off the med, and then take it from there.

For instance I don't see the logic in taking a med that causes excessive and rapid weight gain, (not to mention diabetes) in the name of stability. I would prefer getting rid of the "Omg that couch looks so yummy" pill and try a different one.

I do not however advocate quitting meds without having a back up plan to deal with the the withdrawl and rebound symptoms that are sure to follow.

Doing that is an express ticket back to the pdocs office.

If your son is interested in quitting his meds though, I suggest he taper off them slowly (not the band aid way like I did) while gathering, learning and practicing coping mechanisms, which will help with any aftermath.