It is important to understand the different between biological age and training age. In this case your sons biological age is 14 but his training age is 0. When an athlete is in the infant stage of his training career it is important that he gets on a program that correctly teaches the core compound movements such as squats, deadlifts, and presses. Grooving these movement patterns will set your son up for success later down the road.
As training age increases the specificity and individualization of the program must increase. Right now your sons primary focus should just be on becoming a better athlete through strength and conditioning. His goals should be to gain strength, core stability, explosiveness, and balance and motor control. Also, now is the perfect time to teach him about self-motivation. The sooner he can 'buy in' and understand how important strength and conditioning is the better. It is a process that doesn't always yield immediate results which some people I train just don't quite seem to understand.