Agree completely with Scotty83, I'm only a sophomore in high school, but my trainer(who is also a trainer for SF Giants pitchers) always preaches the training of foundational muscles that allow you to perform basic movements with power and flexibility(lean muscle). Basically make sure that for your son he is not just in the weight room with the team trying to max out and bulk up. On the topic of you putting off pitcher specific training, I would advise that you could start that now. Pitchers train in a way that strengthens the legs without bulking them, use core without losing flexibility, and increase arm strength(while also taking into account prevention of injury). I find(as a main shorstop but also pitcher) that working out as a pitcher is the best way to go. Practice on the other hand can be a different story, I guess that I would just make sure that he doesn't overthrow and mechanics are good. I'd like to say that a rotator cuff workout could prevent arm injuries and a pitcher workout on top of a basic body workout would build foundational muscle. Again though this is all my opinion and what has worked for. Hope all works out for you and your son.