Good advice so far. To add on to the recommendations given I would say focus on simple exercises and work to build a strong base. At that age there is really no need for crazy variations to exercises/drills. He needs to work on mastering the squat pattern, lunge pattern, and hinge pattern, while also learning how to brace and stabilize his spine through a variety of trunk stabilization exercises (think anti-extension/rotation).
At his age the program itself, exercises, sets, reps, etc., is not what's going to make the biggest impact on his performance. It's his effort and consistency. He is at the perfect age to start buying in to the importance of training and preparing his body for maximized performance.
I realize I'm offering very general advice with this post, but honestly that is what's needed. Master basic movement patterns with laser focused intent on each rep and bring a hungry work ethic every single day and you will see the improvements you're looking for.