Alaska in May can be cold, but that's also true any other time. Pack layers of clothes - that way you can be prepared for any temperature range. We did Alaska in May and it was in the 40's and 50's most of the time - 60's one or two days. Definitely bring rain gear!!
I have not sailed either one in Alaska - both are a good bet. The info you have gotten so far on age groups etc. is right on.