I am surprised you have to be 21 for that club. What are people under 21 supposed to do? 18 yo cannot go to the 15-17 teen club and if they cannot go here that's not good. We were on the Carnival Valor in Nov and the disco was 18 and over. They did have security outside the doors. I assume they were checking to make sure no one under 18 went in. Normally I would say unless she looks under 21 they probably will not say anything but since this is spring break and they know a lot of people will be under 21 they may check more closely (or not). I also had heard you had to be 21 to gamble but on the Valor the signs said 18. But then this was a Carnival ship and not NCL so rules may be different. When my daughter went on NCL for her honeymoon she was 20 and they would not let her gamble. In my opinion I do not think she will have a problem but I could be wrong.