We have been going to Key West for over 9 years now and we are both in our late 30's. That being said... I do agree with the previous sentiments about the age and crowd. In the best way possible: KW seems like a playground for EVERY walk of life, so you get lots of (LOTS OF) different kinds of people.. esp straight people. Which is fine, of course. But the Duval Corner with 801, Burbon Street, Aqua, Saloon One, etc... something so wonderful about a gay corner with drag queens and gogo boys!
Yes, it is expensive. But if you can, save up! it's so fun. (And a tip: you can book a hotel or airbnb or something and do DAY PASSES to Island House.)