for me i'll definitely not keep a young big trainee if he's poor in 2 of JS, OD and PA no matter how gd his main skills and potential are.
besides, like wt laker says, keep him or make him an U21 is very probably incompatible. if u decide to keep him, then train as laker advises but a player with tremendous in IS, ID and RB and not decent secondaries will hardly have a chance to make USA U21. then let say u decide to make him U21, maybe he can. but u cant afford him and need to sell him. but at the same time u find that because of his many atrocious and pitiful, he is not attractive to buyers and will sell for a price not much higher than u sell now