My 17 yr old son and his friend had the same type of trouble. They took their cards and they were told they would go into the holding cells.
They followed them everywhere.
The activities staff we found were even a little racial as they let 14 yr olds play in the 18+ games but wouldn't let the 17.5 kids play in it.
I only rated EOS a C also.
Will have to try another cruise line.