It wasn't hot on our cruise so I can't answer the first question, but there are min/max height limits on the Mickey Slide. It is 38" and 4 years old for the minimum on the MIckey Slide. The max height is 64" (5'4"). FOr some reason I think they have a max age too, but I'm not sure on that. I don't know how or if they check the age. My DD (almost 3) was way too short to try anway.
Fortunately on the Fantasy they had a small slide in Nemo's Reef so she was perfectly content and trilled to have a slide to play on.