We did Shark Ray Alley (Belize)on the Norwegian Sun. We had small children probably 7 or 8 on our excursion. My kids 15 and 16 had a blast. I would do this excursion again, again and again. We went to Ambergris Caye for lunch. My daughter was able to find some Pringles for the small sum of 3.50. I almost choked. I think you would really enjoy this excursion. I looked in my brochure from 2002 and there was no age limit. My husband reserved this excursion and I did not realize until we stopped we would be snorkeling with Sand Sharks. I almost did not get in the water. It was amazing. I was able to touch the belly of the sharks.
Grand Cayman we did Jolly Rogers-DO NOT DO & Atlantis Submarine. The submarine was an ok excursion would not do again there.
Cozumel we Snuba was an experience. I am not a fan of Cozumel so really can't help you there.