Keli~ I went on an 8-night Eastern Caribbean cruise in December, and the weather was absolutely amazing (in the high 80's/low 90's). We visited Puerto Rico, Antigua, St. Thomas, St. Maartin, and the Bahamas. Nothing but smooth sailing and sunshine the whole time. I don't know how different the weather would be in February.
We cruised Royal Caribbean, and it was wonderful (despite there being a lot of kiddos on board). I wouldn't think that February would be a popular cruising month for families with kids. My fiance and I are in our 20's and we met several other couples our age. I hear that the premium cruise lines are often full of older folks who can afford the priciness.