Carnival's rules just went affect while Royal Caribbean's ban has been in place longer but has some exceptions.

Carnival Cruise Line takes pride in being a family-friendly company. This is why a certain icon is now banned from its ships.

Must be booked with a relative or guardian (25 years of age or older) in the same cabin or a connecting cabin. Guests 15 - 17 years of age: Can be separated by up to 3 staterooms from a relative or ...