I would agree with Nancy. RCI has so many onboard activities that you teens will never get bored. Plus, RCI requires that older teens behave to a certain standard or they are put off the ship. The last thing you want is rowdy 18, 19 and 20 year olds running through the ship unchecked, I would suspect.
Just my opinion, but I remember cruising with my son Andy when he was in his younger teens.