U18 Manager refusing to play only GK in squad?

Going to try to provide all the relevant screenshots. Not sure what's going on here. This kid has been in the U18s for months now and has gotten in zero games save U21 internationals. He's 16, he's European (no WP issues), and there's no other GK in the squad besides a grayed-out character that keeps getting all the playing time. Rui Costa isn't even showing up on the bench for several of these matches. It's really bizarre, I've never had this issue before with just leaving everything to the U18 manager. It seems unlikely he isn't aware Costa is better than the gray player he's putting in. So what gives? What should I do?

Bah, embarrassed I didn't just search first. Anyway, that did the trick -- at least in the friendly I scheduled immediately to test it. Thanks!

On that note, though: So if I want to have players available for both U18 and U21 I'll have to keep flipping check marks then? Because it doesn't seem to allow players in the U18 to have checkmarks under both.