Rio is winter time, Caribbean is hurricane season. I noticed Tahiti was not on your list.
We are not into sports although we do a little snorkeling. We love our cruise to French Polynesia on the Paul Gauguin; it is a wonderful relaxing cruise. From your list, Greek Islands would be wonderful. I really would look at Regent Seven Seas Navigator. A ship of only 490 passengers that is sailing in the Eastern Mediterranean that time of year. Both Paul Gauguin and Navigator are Regent ships and their website is www.rssc.com.
We are 49 years old and feel right at home on Regent. It is a luxury line that caters more to a younger crowd (all things are relative) and puts more emphasis on exploring the world. I don't think you can go wrong with either French Polynesia or the Med.
Greek islands, Rio, and St. Vincent would be a smaller ship, Cayman Islands does not have scenic beauty (Stingray City is the most unique tour), Aruba is losing tourism because of the Holloway affair), and Bermuda is a conservative laid back island. The best casinos ashore are Bahamas (like the Atlantis). If you like a lot of activities check out the big RCI ships (Freedom, Liberty) plus you might like the grand Promenade. If you want an older quieter clientele, then HAL, or some of the upper level cruise lines are for you.
Freedom Of The Seas -07
Radiance Of The Seas-07
Adventure Of The Seas-05
Navigator Of The Seas-04
Soverign Of The Seas-02
Big Red Boat-93