You might not have had an injury but uve prolly lost 5-6 Mph try to work on a breaking curveball rather then the fastball.
Im 18 and i just recently hyper-extended my elbow throwing a slider. I wont try to through one for 1-2 more years. The slider action is a fast as the fastball with the strain of a curveball, which makes it very strenious on the body. Believe me when i say dont be in a rush to throw a breaking pitch, many good pitchers work on the fastball and the change first.
I would say 15-16 at the earliest. In fact here in australia it is against the rules for a 14 and under to throw any supernating pitch (slider, curve) resulting in fines to that club and points taken from the seniors ladder. The damage to a young persons ability to throw a great fastball is reduced because of the damage to the growth plates in the shoulder of the thrower.
i feel like i said this 6 months ago....