1v1F sets up elastics. It is better for you to train 1v1F until his HA reach high enough 13+ (depending on your U21 Coach desires) High HA trains OD fast, you should always train 1v1F first because it sets up elastics for your player in the future for instance when you begin to train OD.
Also to C-Diddy, I think you should start off with a season of 1V1F to get his HA/DR up until both hits 12-13. You should contact a U21 Scout who is in charge of scouting SFs/PFs and talk with them.
Passing is usually done last because it trains fast on Bigs so you don't have to worry about training PA for awhile.