I'm strongly in favor of mandatory public service. At 18 or when you finish high school, whichever comes last. Only exceptions are actively and aggressively mentally ill, doing legitimately ground-breaking work in some help-humanity science endeavor (which is fairly public service anyway), and maybe really essential to family support (parents both disabled kind of thing). But educably mentally challenged, potential athlete, rich kid -- yep, gotta go.
Wendy P.