10U
12U
15U (u = and under)

I pitched as kid.

Accuracy is more important than the types of pitches (FB, Curve, slider, etc.) Have him get the mechanics down first. Then practice accuracy. Set up a box (size of home plate on a chair. Pace off distance and have him practice throwing the ball into the box. Once he can start hitting the box on a consistant basis, then start working on speed/throwing harder. Do not attempt to teach/let him try "fancy" pitches at this age. Curve ball, split finger, fork ball, and all the rest should be taught by coaches with experience, and only when the arm has "matured". (No, with the 10 and 12U I did not stress/teach anything but accuracy. With this year's team, I have some 15 y/o who may be able to handle more advanced pitching techniques. However, after watching the last pitcher/catcher practice, I think it'll still be accuracy that will be stressed.)

All leagues under 12, pitchers can only pitch 3 innings. 10U no stealing home. 10U and 12U no leading off. 15U regular baseball rules, but pitchers are limited to only 1 game a week.

Good luck.