I don't know of any, you may want to look for group bookings through the sites that cater for that age range.

Are you specificaly looking for a ship full of that age group or trying to avoid a ship FULL of older people?

We have found that there are enough choices that attract a wide rage of ages so there will be enough people to mix with and not feel out of place.

The only one I can think of is Easy Cruises.

luci

From reading some reviews(cruisecritic) easycruise is becoming a bit of an all age groups option and not the backack/young cruiseline we thought is would be.

Also atracrting Americans with the greek/turkey options.