Biggest risk factors were playing year round (they recommend taking 4 months off per year), and pitching frequently without being engaged in a good arm care program.
That being said, you don’t have to throw a curveball to be effective as a 12 year old. Being able to throw a good change up is huge. If you can change speeds effectively and hit spots (google Perry Husband’s Effective Velocity) you can dominate.
My 11 year old throws up to 63 mph (just gunned him yesterday), but he has a great little knuckle curve that he dominates with. So much fun to watch.