i started at 11. probably should have started earler than that
i have had no problems with height, even after squatting and deadlifting maximal loads. im at least 2 inches taller than most people on both sides of my family so that shoots that theory to shit
i've reaped the benefits of training while having raging hormones, and i still get to do that for another few years
its just like teaching a 30 y/o how to train. show them proper form, example workouts, nutrition, and the right, positive, helping attitude that keeps all of us going