14 is old enough to take instruction well. I taught an young man last year about that age, and it took so few flights that the first airplane he bought was a Twist. He has done well learning the basics, but now is going through finding out just how many ways you can make a mistake.

When I was that age, I had been building from kits for about 6 years. When I switched from control line to RC, I soloed on my third flight.

I have taught as young as 10, but find it much easier once they reach 14. If I were you, I would start looking for his next airplane since he will pick it up very quickly.