Nothing good can come of making calls too quickly. You need to see that the fielder has control of the ball in a force situation and then make the call. On a routine call where the runner is out by a wide margin, I do wait for the runner to cross the bag, just to keep my timing. At 14, your son may encounter problems based on perrceptions because of his youth. He needs to look like an umpire, and make his calls like an experienced umpire which will help to keep the idiot parents and coaches off his back.