Solent/LHD, that is exactly why I never did a program like this with my son when he was in HS. There is something called a biological age that varies wildly with kids and I personally would not recommend one of these programs for an biologically young player. Personally there is so much to be gained from the proper throwing program, instruction, and strength and conditioning that IMO until these have been perfected and developed I would wait, plus there is the issue of proper instruction. and I am sure that, like weight lifting without proper technique, you can do more damage than good.