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I have been on the Fantasy many times and absolutely love it! The ship has been refurbished multiple times and looks amazing for her age. As others have said, and I agree with - Carnival has plenty of seniors! Oftentimes they will be the largest demographic on the ship. Of course this varies with the time of year and itinerary. This will be most likely the case for a Bermuda cruise from Charleston.
Cruise Director Risa Barnes is also an acquaintance of mine, and told me the same thing that Jabee noted about the Bermuda cruises.