Its not as dangerous and risky nowadays. If you teach it right and the kid has had a pretty big growthspurt already, he'll be fine. I started throwing one at the age of 10 after a little growthspurt. Im 16 now and I'm going to be playing some Varsity this year because it's a good curveball. I have never had any shoulder pains at all. Just work out right and when your arm hurts, you need to run to get the lactic acid out of your arm.