You should checkout
www.singlescruise.com to see if any of their departures are the cruise you are interesed in. They have a robust onboard activity agenda (singles mingles) but if you dont want to participate its fine. They can tell you the mix of passengers--age & gender if you are interested in the group activities, dining, shore excursions, etc.
If you just want to cruise alone, still call Singles Cruise because they know the cruise lines and ships that accommodate single guests the best.