Retired, no kids at home, no pets.
Seven days generally isn't worth the trip to and from the ship, and we've felt that way since long before we retired, although we have done an occasional seven day for specific purposes (getting together with old friends, etc.).
We average between 12 and 16 days.
Norm is right, though: if your horizon is limited to the Caribbean and Mexico, seven days can make some sense for some people. If you ever branch out to overseas itineraries you'll be forced into longer voyages, and you'll probably discover that you're not "ready to go home" after a week, because the places you visit are far more varied, exciting and interesting.