We've been there, the first week, twice, and thought the weather was pretty nice, especially coming from NJ!
Last December, I wore shorts, capris and jeans with t-shirts (not all at the same time!). The night we went to MVMCP, we were in jeans and t-shirts the entire evening...didn't need our jackets! We had some days in the 80s!
A couple years ago it wasn't so warm, but it still wasn't cold. We only wore shorts one day, with jeans and t-shirts the other days. We did wear our lightweight jackets at night.
I've never been there other than the first week, but I thought the weather was pretty nice, especially when, here in NJ, they were hit with a snow storm (the first time we went) and last year, we left in an ice storm and came home to snow!
Not to be a wiseguy, but don't most elderly people move to Florida for the warmer winters? If you're planning on going the first week or two, I think you will be ok.