Casinos are very tightly controlled. Case in point: on many ships you have to walk through the casino to get someplace else. That is fine as long as the minors keep walking. My son was with me once and I stopped to put a quarter in a slot on our way through to a show. Before the slot machine stopped spinning I was approached by an employee and reminded that minors were not allowed.
The bar staff can lose their jobs by serving minors and all it takes is one violation. They have always been quite strict in my observations.