Hi,
sorry, I didn't read all the answers to your post and maybe someone posted something similar, but here it goes:
2 weeks of ID
2 weeks of RB
1 week of IS
1 week of 1 on 1 for SF/PF
Train like this until his ID and RB are 13, then train 1 on 1 for SF/PF only. He should reach his potential before end of his 21 years. IS and ID should be trained one positon (for C and not for C/PF). He should get 48 minutes per week on trained position.