You know there is a limit number of players that may train at a team, the number is 42.
I do not know how this number was calculated. But right now, for teams as mine that compite at every age it has became very low.
This number means that you may have 14 seniors, 14 U23 and 14 U21 players.
But if I want to train player for any age (19, 20, 21, 22, 23 and seniors) just to be competitive at any season, then it is impossible.
I do not say that the number has to be change, but maybe it is something to think about.