Hello Brsevgi,
Estherderu is correct. If your physio is used to children and teenagers and knows sports physio, taking their advice would be worthwhile. I have provided a few thoughts for you in the mean time.
Cross training with pre and post stretching of the opposite muscle groups used
during the exercise is very important. Most highly successful sports people are excellent in one sport and very very good in a second sport. Cross training early in life fine tunes brain training allowing movement patterns that can be used in unusual circumstances. To be an expert in any field it is commonly accepted that 10,000 hours of practise is required. This can be in matches, practise games or even just bouncing the ball. Most good sports people involved in ball sports are rarely without a ball in their hands. The brain is integrating skills all the time.

If an examination of the sports done seems to use one side of the body more than the other eg left / right or front/ back then specific training drills or weights program can address the imbalances. As your son is only just having a growth spurt heavy weights are to be avoided to protect the growth plates. Light weights for endurance and flexibilty would be acceptable - rubber band or tubing eg theratube / theraband or similar brands could be used.
Be aware that it is unlikely that any overtraining problems would occur in the short to medium term, however the damage will be cumulative and is what eventually shows up as nagging injury that may eventually end a promising career before it has even started.
Most important, as you are aware, is to know if he loses interest and if so, why. Knowing why is important as he may want to continue but something else is worrying him OR he may really want to do something else.
Occasionally outside help from a good sports psychologist can sort out glitches. Teenage years are notoriously difficult for parents to sort out such problems.
I hope some of the above ideas will help your son.
All the best for the new year.
Regards,
MrPhysio+