I do not know how the high school is in your area, but I would start training him at 13 just to get him in good form. The high school my kids went to made it mandatory for all students in sports to have a weights and conditioning class, so yes, if you did sports all four years you had weights and conditioning all four years or you could not compete. The teacher here was not exactly the best at his job and my son would argue with him constantly to the point my son, a three sport varsity kid, was getting a C in the class. He always explained, "I train with my dad and he says my form is fine." Where the teacher disagreed. I set up a meeting and as soon as the teacher (5'7" 165 lbs 20% BF) sees me (5'9" 220 lbs 8% BF) he realized I probably know what the f*ck I am talking about and he let my son do whatever form he wanted for the rest of the year.