Chan, I will go out on a limb here and try to answer some questions for you since you haven't received a reply yet, but I should warn you that I have only done the 7 day out of Seattle on Princess. But based on the reaction from the shopkeepers in Alaska, and the fact that they have been sailing Alaska for about 30 years, I think you should really consider Princess. They just built several lodges exclusively for landtours. There were lots of kids on Princess, but they were very well behaved, and we really didn't see many in the alternative restaurants.
All ages were accounted for, but the mean was 30-50. A hairdresser on board who has done all the cruise routes said that Alaska is now the youngest group, at least for Princess. (She said she had never done so much white hair in her life as she did on the New England tours!) But a cruisetour would probably have older people on it, since it is a longer tour.
I have read that people suggest taking the south bound route, ending in Vancouver. That way you have less time zones and distance to cross on the way home. This seemed especially important to people from the east coast.
I checked the airfare from Anchorage to Vancouver, one way, and discovered that it was about $400! But if you look on the map, it is about the same distance from Anchorage to Vancouver, as it is from Vancouver to Houston! Since it is one way, it may be better to get the air for this leg through Princess.
Please post a report when you get back. I really want to make a cruisetour the next big vacation that we take and would love to hear about your adventures!