This is call good, and probably doing wonders for him socially and psychologically. As I noted yesterday however three games in four days is a lot, and he wants to start going to the gym as well.
Here are a couple of articles I picked up to help me make sure everything stays on the straight and narrow.
Should my kid lift? Part 1: The science says yes
Should my kid lift? Part 2: Principles for developing fitness in children for sport and life
Advice for fourteen and fifteen year olds is "progress to more advanced resistance exercise programs, add sport-specific components, emphasize exercise techniques, increase volume," but the money quote is:
Notes: Any kind of CNs training should NOT come close to leaving a child exhausted, beat up or excessively tired and drained. If this is a regular occurrence, check in. Especially if your kid also plays a sport.