Go for a cruise line specifically aimed at your age group with entertainment options that are designed for the more lively late nighters. Ocean Village would probably fit the bill. The two ships have lovely itineries in the caribbean and also benefit from avoiding a US gateway such as Miami. Getting into the USA is dreadful and well worth avoiding. (RCI etc). Direct flights to and from Barbados are excellent ! PS. I havnt been on board but my 26 yaar old daughter has.
The majority of cruisers are still of a more mature age To ensure a lively time you need to go at peak holiday times especially US holidays eg Easter, July, August, Xmas/New Year. This applies to all cruise lines.