When I went on my senior cruise a few years back, we went on the Carnival Cruise Line's ship "Holiday" - it was awesome, and the service was excellent. I'd definitely recommend that line again.
/ We went to Playa del Carmen, and 3 or 4 other spots in Mexico. Since I live in Memphis, the closet place to here to leave out of was New Orleans at the time, so that is the location we boarded on. I had an excellent time and would definitely recommend them again. Good luck finding the right cruise for you
. (Oh also, when you get there, be prepared to wait a good while in customs if you go out of the country- we had to wait 3 hours because there were so many people. But other than that, it was wonderful).