The type of routine he is doing, the intensity, his diet, all come first.
I used to use supps at 15 as well, mainly just protein powder, that's all the local store really had.
But I ate a ton (Italian Mom) worked out like crazy almost daily (Arnolds Encylopedia) and always went to failure.
(Not all good advices these days, but this was 1981).
Throw in Hockey Traveling team, and I was never sitting (again, different times compared to today, most sit around playing video games and phone diddling).
At his age (and level) Supps wont do anything. Correct diet and training and giving it 100% will.