Hi, Jennifer!
Congratulations on being of the first cruises to set sail this year aboard Disney's
Dream! Your family is going to have a wonderful vacation sailing on Disney Cruise Line's newest gem of the sea.
As far as water skiing, I am assuming that you're talking about the
Watercraft Ski Adventure on Disney's Castaway Cay. This is a guided tour of the waters surrounding the island aboard a "Waverunner." I also have a 16-year-old son, and we had to deal with his disappointment of not being able to drive one of these watercraft because of his age. The rules for this excursion are firm since its a safety issue, but of course, your son is old enough to be a passenger -- if you have an adult in your family who will drive him.
For our family, we decided to let my son enjoy a kayak adventure by himself -- which he enjoyed. It satisfied his desire to be alone on the water. I hope this helps give you an idea of how to entertain your teen son.
Have a wonderful day and a magical vacation. Bon voyage!