Hi, Thayer!
Go ahead and take the plunge -- cruising with Mickey is such a fabulous way to please all ages in your family! I, too, have a big age gap of children in my family -- from 17 down to 7 -- and we've been on Disney Cruise Line vacations for more than four years now. From teens to toddlers, they are all adequately amazed, entertained and awed on each of their levels by everything on the ships as well as where we've traveled by way of Disney cruises.
In addition, Disney makes it easy for families to stay together, too. On occasion, my teens have joined their younger siblings in the Oceaneer's Club and Lab for fun activities and events together -- as well as the 7-year-old tagged along one afternoon with my 11- and 14-year-olds at Edge when they built castles made of uncooked pasta. We often allow one or both of our older children to take their younger siblings to a movie or to an event such as a game show or karaoke. Armed with a wave phone, they are only a phone call away, and we usually decide on a designated time and place to meet up for occasional "check ins."
I hope this helps convince you that out of all the ways you can spend your vacation resources -- time, money and effort -- a Disney Cruise vacation is a wise investment in your family's memories and experiences. Please let me know if I can help you further -- you can find me
here with my "ears" on!
Have a wonderful day and a magical vacation. Bon voyage!
Andi