rocket - Come on...now you're arguing nits. Virtually no one would disagree that a well-conditioned arm is less susceptible to injury...not immune, but less likely...just like other parts of your body.
Honestly (and I'm not making a judgement here, just expressing an opinion), but its hard for me to see why a 12-year old touching 80 mph would need anything but a fastball. What does he gain by throwing a curveball?
The kid in our area who threw the most as a youngster and threw a fair (not tons) amount of curveballs at a young age just had TJ surgery. Did the pitch count or the curveballs get him, or did something else? He has great mechanics by the way, and no one would say his arms wasn't in great shape.
And then I remember some comments a year ago when a very high profile freshman pitcher at a top-25 school had TJ surgery. I believe PGStaff had some comments based on their previous scouting of him that in part wondered why he threw so many curveballs to go along with his 90 mph fastball in HS? Seems like they had an inkling of what was to come. I saw him pitch before college...best curveball I have ever seen for his age. But he threw it a lot. Did it cause it/contribute to it? I don't know...but I know a lot of people think it did.
Again, why take the chance?...we're talking about a 9-year old! I just don't get it.