I was like that when i was 17 for guddsake... Everyone has to do the growing up first hand... I think it excellent your giving him advice... but remember give him the chance to make the mistakes, and learn...
I used to be really into just general pop crap at 15.. so i had a very late start in music... I made the mistakes and learing, and i know there's more mistakes to be made...
I say go for it IH, but dont throw in school... you woulnd't believe how nice school is till you quit it... even if you dont enjoy it, it give you some stability, a constant social life... there's very little to gain from quiting at 16 rather than 18 or even later... Why dont you go for a lot of music related stuff in school...
I think, with all due respect, that your too young to really form an oppinion about what field you really want to go into yet.. take your time, although poeple talk about taking your chances, in life it's really more about doing your work and knowing the right poeple..