It's depending on the need of the NT, which the manger of NT want his team to be. But for my side, since i electing for U21, i'm looking to build a balance team, and for U21 there are only few season to train, so it's setting a idea skill set for u21 player is not really a good point.
So like i say, the team will discuss, see what does NT, U21 and the club need, so we would train the player due to the need of this 3 point, but still for those skill that are better to be train when young, we will try to concentrate on those.