This is a fairly serious problem. In my current custom cup, which was specified as a youth cup for u21 players only, almost every team has used overage players. Usually there is at least one team that does this, but it seems to be getting worse.
This situation is easily addressed in friendly competitions, since teams that break the rules can be penalized points or even disqualified from the competition. This is not possible in custom cups, however!
Custom cups need a youth option when they are created, that would prevent the use of players age 22+ whether intentional or not.The only other recourse is to keep track of teams that break the rules to prevent them from joining future cups.
For now, can we at least get a new "Child board" for blacklisting teams that break youth rules?