I think the Alaskan trips attract an older crowd, or at least a crowd with multi generation families. On our last trip we were on a shuttle from the cruise terminal to our car. There was a group on the shuttle with 4-6 late teens to early twenty's. There were complaining about all the old folks on the Carnival Spirit.
We were on the Holland American Zaandam. It was an older crowd but there was a mixture of families aboard. We loved the cruise, it was a 7 day round trip out of Vancouver. Have also been on the Sun Princess out of Seattle. It was also a 7 day round trip. We enjoyed the itinerary of the Zaandam more. The both included Skagway, Juneau, Tracy's Arm and Ketchikan. Hal also did Glacier Bay, it was beautiful.