1. Fundamentals (age 6-9) focus on physical literacy, gross motor skills
2. Learn to Train (age8-12) learn overall sport skills
3. Train to Train (age 11-16) consolidate sport skills + tactics with physical abilities
4. Train to Compete (age 15-23) sport specialization, increase training intensity
5. Train to Win (age 18+) focused, dedicated, competitive
If you really want to reduce ACL injuries, "Tommy John" surgeries et al follow these guidelines. Quick fix protocols later on only have limited success.