Would my 21yro pg/sg or combo whatever be able to be in u21?
You should ask femit. He is the U21 coach.
I would give him some 1v1 Guards training until his HA/DR is at sensational or tremendous. Then I would also train his OD to wondrous, since this is the lowest level of OD the U21 will take.
Due to the depth of players we have that can play for the U21, your player may not make the cut. Good luck.