Making U18 players available/unavailable for U21 games ?

[VinnyChilds]

I'm primarily concerned with the 'unavailable' part of this. I have a small squad made up of 26 'seniors' and 11 U18s. I generally only make the seniors available for the U21s when they need match finess (and they're not too old), but the rest of the team gets filled with my U18 team. As a result, they play their U18 game on the saturday and an additional one midweek. By the end of the first month they're knackered, I'm now having to manually move them all to the senior squad before the U21 game and back to the youth squad once it's been played to prevent them playing midweek.

Is there some staff responsibility I'm missing regarding which players can be selected for certain squads? I'd really love a right-click>make unavailable for [selected squad] or something, or an option to only select players from within their designated squad. The only other option I can think of is to move them all to the U21 squad as default and let the U18s fill up with 'ghost' players, but I'm unsure if that would affect their U18 training.

Before anyone says 'rotate more' or something, I'm doing that with the seniors, especially when we're playing midweek first team games. Besides, making a senior available for a wednesday game pretty much rules him out of the first XI on the following saturday. Normally I don't enter U21 groups for this reason, instead booking my own Monday friendlies for them, but as this is the first season I wasn't given the choice.

[mack4ever]

Move your U18 players into the U21 squad.

Unless I'm remembering this completely incorrectly, players from the U18 can be picked for the U21 team by the AI but players from the U21 cannot be picked for the U18 team.