Many bones in a younger body aren't fused until late adolescence, most famous for archers is the acromion, the two piece bone you can feel at the top of your shoulder. Heavy manual labor or pulling a heavy bow keeps them from fusing so examinations of medieval skeletons of archers often show this phenomenon, however, modern adults not subject to intense shoulder stress will have them fused. As a young (or any age) shooter, your biggest risks are a ligament sprain or a muscle strain. Both are basically tears to the tissue. When it happens, you need to stop and let it heal, period. Use ice to start, and Advil for inflammation. You can take some basic steps to help prevent this by properly warming up your muscles and joints before shooting. Muscles are heated by blood but your joints need movement to get the synovial fluid moving and lubricating. Just common sense right? Long term risks include tendonitis, bursitis, osteoarthritis and other over use injuries but if you take things slow and let your body adapt, it will. By the way, I'm 49 and like I said, I can easily handle my #120@32" but it took years to get there.
