So guys I recently started doing squats and my game has improved immensely from it (feel much more explosive and better on ice). So one of my friends who is training to play in the OHL (top junior hockey league in Ontario) says that he can't do them because when he was younger he broke his knee and it hurts when he squats and he also experienced osgood schlatter when he was growing up (back a few years ago).
Also his dad who used to be a body builder (21 inch arms before he tore his bicep and had to slow his training down) says that you shouldn't do them as they shrink your spine while you are still growing (both of us being 17 turning 18). Anyways I am probably going to be training with him all summer and I feel that it would definitely improve his game if he were to start squatting, is there anything I can say or show him to convince him that he should start squatting? Note: He isn't opposed to leg workouts (he does a lot of work on the leg press), any help is appreciated.