I started flight training at 15. In fact, I learned how to fly before I could drive a car. 20 years later and I'm still at it. As long as he stays motivated, he'll do just fine.
Also, as I flight instructor I agree 100% with John regarding the use of MS Flight Simulator. Bad habits are often 10 times more difficult (and costly) to unlearn than it is to learn something the right way from a flight instructor the first time.