We are going on Ren to Tahiti in Aug. Our first cruise with Ren. Don't know about the younger, more lively crowd, but dress is more casual - no formal nights. "Country club casual" is what they say. Ren doesn't have the exciting night life that most cruise ships have. Our itinerary is port-intensive and everything I've read said no one is up after 11 pm -- too tired. I'm not sure about the age, I've read everything from mostly 30's to 60's. Guess you have to decide what you want. Check out all the different message boards to get a good feel for the ages on board.
As for me, I am greatly looking forward to being in one of the most beautiful places on the face of the earth!!!
Gee, its really a shame that Carnivore Lines doesn't "do" Hawaii or Tahiti yet. They certainly cater to "a younger more lively crowd". But then, so do LegoLand and Chucky Cheese Pizza.
Perhaps Disney would consider creating a ride in one of their parks that merely simulates a cruise. Instead of having to actually travel with a bunch of nasty old AARP Commandos, it would be stocked only with funloving beautiful people, just like you, who don't "like to enjoy the view!".(No offense.)
Come to think of it, there are already some pretty good video games and virtual reality simulators, so you might just be able to play "let's pretend" with your Play Station without leaving your room.