I just got back yesterday from my first singles cruise, on Carnival Legend to the Southern Caribbean for 8 days. I went through CruisingForLove.com - they have many singles cruise options to choose from. My experience was fantastic- our group had about 40 people and the age range was mostly in the 30-50 range, with a few outside that range. Most of us had never met but we had a BLAST! We bonded quickly and had so much fun the whole week.
Since you have apprehensions, I would recommend that you NOT room with a male - that will eliminate one of your concerns. Ann (at CFL) will find a female cabinmate for you on the cruise you select. I know several of the ladies in our group were paired and I did not hear of any problems - most seemed to like their arrangements.
I had originally planned to share a cabin, but because I booked late, did not find anyone, and ended up in my cabin by myself. I did pay a little more, but also my rate came down at the last minute before I booked so it wasn't too much of an increase for me over a shared cabin. I found that the convenience of NOT having a roommate was well worth the extra money I paid and will probably do that in the future as well.
For what it's worth - I am a swm, 40, in the Tampa area. I am hoping to go on another cruise this summer - June would work out well for me. Feel free to contact me at firstname.lastname@example.org
if you have questions or would like to chat further about my recent cruise experience or the possibilities for this summer.