hey...
I would train them as a PF or a SG with decent inside skills. I have been training guards since I started the game. Training OD is the slowest skill to go up and inept and pitiful, are really not worth training up. In my opinion... 20 is actually even too old to start OD training. If you want to make SF you should train OD when a player is 18 and 19 and not at 20 and 21...