I went on a Cruise once. It wasn't one of the hip cruise lines, so there were a total of maybe 10 people under 30 and 1000+ over 60...
There is nothing to do on a cruise but eat and have sex. The 10 or so young people went nuts. One guy had a threeway with a couple of 15 year olds. Mostly everyone else just cheated on their long term boyfriends and girlfriends... If you don't cheat, I recommend
you bring a lot of good books.
Good food though. Might be fun to do with your partner.