re: 11 yo son started lifting in gym.

My only observation is instead of a bodybuilding style workout I would focus on mastering the traditional full body/compound lifts. Also I don't mean mastering like many/most middle-aged novice lifters do in the gym, I mean focusing on form first on every single rep.

I think lifting is great for young athletes, but while not easy, people with a good athletic base generally have no problems getting stronger as they age. What is much harder to develop and maintain as people age is mobility, explosiveness, and balance.

I would focus lifting reps on compound lifts and include a mobility session with every gym visit.