Additional thoughts:
Lots of cruise ships call at Key West; you could look at them.
Your not-quite-21-year-old son can present his no-alcohol status as being due to taking his turn as “designated driver”.
It’s worth it if you enjoy clothing optional and have had to do without, due to lack of such places in the Keys. Get a quick fix, plus look down on the streets of Key West with no pants on whatsoever.
Plus, lots of nice body painting can often be seen. Very artistic. A body painter is often up there, and you can watch 'em work. These same artists are the ones that paint a lot of folks up for Fantasy Fest.
As a bar, well, meh. I don’t drink anyway. The music didn’t suit me real often, due to a dearth of classic rock.
Ft. Zachary was indeed very nice. The historical bits were very interesting, if not as impressive as Ft. Jefferson. The beach was lovely, the best on Key West.
As for kink shops without dad, go to Fairvilla. The Mrs. nearly maxed out one credit card there. 
The Garden of Eden is on top of a two story building with a bar on each floor (Bull and Whistle are the lower two floors) so it’s worth a visit. It’s hit or miss. Personally we’ve never done the nude drinking thing because the mood was never right. Either it was empty, or there were a shit ton of dudes hoping to see some boobs. It’s on a rooftop, so you can get some sun during the day. They have a DJ at night and really enforce a no cameras policy. They also do body painting.
I’m only aware of one fetish shop (Leather Master!), although there’s a lot of places that sell adult items. There is this weird, creepy escort place on upper Duval. You’ll know it when you see it.
I don’t know Florida laws, but it’s a safe bet there’s no legal way for the >21 to drink.
Some other things I thought of: If you’re up for a movie, check out the Tropical Cinema. They show feature and art films, and you can get a bottle of wine while viewing. If anyone’s into fishing, there’s some good stuff in Key West, and a lot of restaurants will cook your catch. Ask someone about the cruise ship schedules and plan accordingly. There will be several thousand extra people on lower Duval.
Key West is a fun place to explore. Every time we go, we discover something else. Keep an eye out for the Key West chickens.
I would recommend the seaplane to the Dry Tortugas. First off, it’s a fricking sea plane! Landing on the water is an amazing experience. Secondly, the fort on the Dry Tortugas is just an amazing piece of architecture and history. It’s also a bit of a birder’s paradise, if you’re into that.
Got my first tattoo at Paradise Tattoo in Key West. 
And…you really gotta check out a drag queen show. It’s an experience!!
Don’t hassle the federally protected chickens!!!
takes the Shake and Bake out of her suitcase
Lots of good advice upthread, and I don’t hang out in Key West all that often, so I’ll just address this…
You can’t legally buy a beer for someone under 21 down here. I certainly have never done that. And I certainly haven’t ordered an extra beer for myself, while distracting someone’s parents.
I also certainly wouldn’t encourage you to do anything that is technically illegal.
Ack! I’m >21. Do I need to get rid of my kegerator?
One thing to do that, surprisingly, no one else has mentioned. Drive north three or four hours to meet up with a few South Florida dopers!
It’s been mentioned a couple of times already, but really needs to be stressed. You simply MUST eat at Blue Heaven if you are into good food. There are things I would do for their Carrot Ginger Soup recipe. Dirty, evil things. 
Nope, I looked it up and Florida is not one of the states where you can buy your kid a beer at a bar; you can’t even serve them in your own home under your own supervision, unlike my state (Illinois). Since we rather like his financial aid package, we’re not going to risk that.
I wish I had taken a plane out to the Dry Tortugas. I took the “wide, stable” high-speed ferry…on a windy day with a 3-5 foot chop. Even with Transdermal Scop patch, it was a rough (but very cool) day.
I knew I’d screw that up. You can keep your kegerator.
It’s great for breakfast, but there can be a wait. The setting is great, too. It’s mostly a big dirt courtyard…with a ping pong table!
If you need groceries delivered, try Faustos. Pricey but good.
At the upper end of Duval is a pier and a very small beach (South Beach). It looks like it’s part of the Southernmost Hotel, but it’s a public beach. This is where the Southernmost Cafe is located. It’s a nice little place for breakfast or drinking on the beach.
Key West Bar Card - $20 for a card that gets you 2 for 1 at select bars. You can use it at all the participating bars once a day (never used it, but I know a lot of people swear by it).
The Bull, Whistle, and Garden of Eden website. - Printable drink coupons for each bar!
Go see the turtle races at Turtle Kraals.
BTW, screw those roosters! Nothing like a crowing bird right outside your window at 3:00 AM. Nothing quaint about them.
Best chicken dinner I ever had was in Bali, home of free range roosters. The food was good; the knowledge that there was going to be one fewer crower on the block…priceless. 
So…straight guy here…but no one has mentioned gay culture? Drag shows, gay bars, AIDS memorial, etc. The drag shows can be great fun and the great thing about KW is that no one gives a crap whether you’re straight or gay–and going to a drag show is probably something you’re highly unlikely to do at home (b/c there people DO care if you’re straight or gay).
On the complete other side of the coin, I remember a Catholic Church or something that had a walkway rosary. Very cool too.
You must eat at Rick’s Blue Heaven. When work and cold weather get to me, I imagine I’m having a lazy brunch there…
If you are driving down to Key West you go right by (150 feet) the real live African Queen from the movie of the same name.
Just as you are getting into Key Largo (right on the north end of the keys) it’s on the right. Worth a look and there’s a couple of restaurants right there so you can justify the stop with lunch.
Damn, I missed this when we went last year 
How did I not see a sign or notice it mentioned online when I was researching touristy crap for our trip :smack:
[And I love the movie Key Largo with Bogart and Bacall and classic Hollywood Noir, I really did look online for touristy stuff to do when we were driving through.:(]
I took a biplane ride there that was alot of fun. The guy takes you up & cruises around the island pointing out wrecks and other points of interest. There was also a guy who would take you up in an ultralight. It was a pontoon plane located in the bay to the right of the main road into town comming from the North, if Im remembering right. Should be easy enough to find if you’re interested and hes still there. This was probably 7-8 years ago. Second finding the beach at the end of duval street. on the opposite end from the square. Much nicer than the more well known Smathers Beach I thought, and with the beach bar/restaurant right there, its a very nice spot!
So, this trip has been insane. Totally insane. Beginning with the first plane out of Chicago, which was delayed an hour and then grounded for mechanical failure. They found us a new plane, but of course we missed our connecting flight in DC. Three “ain’t gonna happen” standby flights later, and finally got put on a flight to Miami that got us in at 10PM (instead of noon). The rental car place was long since closed, and I wasn’t going to drive through the Everglades in the dark anyhow, so the airline gave us a voucher for a room…a room. Four travelers, two parental units, an 8 year old and a 20 year old. After promises at the airport that there would be two beds in said room, we got to the hotel, where the last room available was a single King. This was, by all accounts, the last room in all of Miami. After 20 minutes of phone calls and no cots and wtf, a nice young lady checking in traded us for her double Queen room.
Next day we waited an hour for a cab promised in 5 minutes, which took us to the car rental, we get the rental car, which has a big dent in the driver’s door. No biggie, it’s drivable, I don’t care. Traffic delays, blah blah blah… got into Marathon only 28 hours behind schedule. Far too late to sail to Key West. No problem, we’ll leave tomorrow.
Tomorrow, the bilge pump on the boat fails. Several hours fixing it, and the weather turns sub optimal for sailing. Captain (Dad) nixes the sailing portion of the plans.
No problem, we’ll just turn Key West into a day trip! Go on the shuttle bus, which breaks down on the side of the road 3/4 of the way to Key West. :smack:
You can’t make this up, people. So far this trip, we’ve dealt with a messed up airplane, a hotel room, a rental car, a boat and a bus. Let’s just say I’m not going to book a helicopter tour any time soon.
Nonetheless, we did manage to have a lovely afternoon at the Dolphin Research Center in Marathon, where the smaller WhyChild and I got to pet a pair of dolphins. Today we eventually made it to Schooner’s Wharf in Key West for lunch (the jerk chicken sandwich was excellent), and spent a day wandering shops and deciding the line for The Hemingway House was way too long to bother with. But we did enjoy Mallory Square very much. Little one got henna on her hand, big one got some gifts for his girlfriend. We finished the night with a really great dinner at the Cuban place in the square, whose name I never learned. The Tangerine Dream drink was devastatingly delicious, and the food top notch.
I couldn’t remember where the butterfly place was. 
Maybe we’ll go back. Probably not, it’s a two hour bus ride even when the bus doesn’t break down.
So, learning a lot this trip about flexibility and making the best of things and enjoying the journey at least as much as the destination. But it’s not at all what we anticipated, and the Key West vacation is now pretty much a Marathon vacation. Hey, it could be worse. I hear it’s 15 below in Chicago today, and I’m sitting here on the deck of a beautiful boat in my shorts at midnight. Life is still pretty sweet. 
You can still catch the drag queen ringing in the New Year in her giant fuck-me pump.
This is sounding like a Florida version of Planes, Trains and Automobiles!
If you see any Publix supermarkets, their Key Lime pies are quite good and you don’t get stuck paying tourist prices for it.