just a piece of advise here
if u are going to train OD on a big, first give him a full seasons of 1v1 on SF/PF position. that will make his DR/HA go up (a skill which is usefull on any player, regardless of their position). However, the biggest benefit of having a high HA/DR is that it will speed up the other guard training.
So if u do 1v1 on SF/PF, u'll get 2 (or 3) pops in JS, 5 in DR, 4 (or 5) on HA, 2 (or 3) on IS and maybe some other random pop. the free IS is always nice to have. The JS is free too, and comes in handy aswell. And the HA/DR will influence the quality of shots he takes (and the shots he creates for himself).
Now after that, u do a season of OD ==> because the HA/DR is already pretty high, it speeds up training on the OD. u'll need about 2 to 3 weeks less time in traniing OD than u'd normally need. his Od his lvl 9 (should still give u some time during that second season) and then u can train your player as u deem fit (i'm assuming u'd like to have a Power Forward). also, the OD trainign should give u 1 (or 2) pops in ID aswell.
With HA/DR&OD (and probably a slightely elevated JS) u could train PA if u'd want to ( PA on bigs is never a bad idea) or u could start the inside traniing (RB/SB untill he caught up with his IS/ID lvl and then train each one of em till they hit lvl 9)
that should give u a nice Forward for the U21 team, it also will keep your salary low (always interesting from the economical point of view) and the biggest chunk of outside traniing will have been done, meaning that you probably need to focus on inside training (and the occasional 1v1/Jumpshot training on SF/PF).
i'm speaking from experience here. i've trained up Kaiser ( a forward). given him a 1.5 season on 1v1 on SF/PF and he's matching the same speed as my guards in terms of popping on OD&JR, despite him being considerably taller and thus should be training slower (i'm also beating the time predictions on when he'll pop according to 3 excel files that i got concerning the popspeed he should have with the lvl trainer that i have).
either way, it's just a suggestion. if u like it, run it by the U21 coach before applying it. i'd hate to contradict him, he's still the man in charge of the U21 ( and the one who has the power to select players for the U21. sometimes u got to many forwards already and thus prefer a guy being trained as a C for a generation, so whatever u do, run it by him first ;)
regards
Az~