Yes, I'm a 36+ year old man who wears Heelys. In fact, I love my Rumble (#7317) Heelys so much, they are my primary shoe. I don't wear the wheels in all the time, but sometimes I'll put the wheels in and heel around the house. Usually I'll bring the wheels with me whenever I go somewhere, and pop them in whenever the opportunity to roll comes up.
It all started in November of 2007. I had decided to get my sons both Heelys for Christmas. Knowing that they'd be heeling around whenever we went somewhere, I decided that I didn't want to be left out of the fun, and so I got myself a pair. My first was a pair of Escape (#9110) Heelys. I didn't know anything about them, really. I just found a store that claimed to have adult size Heelys, I went and tried on the least offensive (I detest brightly colored footwear) pair they had and bought them. Fortunately, they were on sale as well. As it turns out, I bought a style that uses Mega style wheels, which I was told later on was a good thing.
As is my nature when embarking on a new hobby, I searched the intarwebs for a community to partake of and participate in, and I found that in HeelyChat.com. There I found a lot of helpful heelers, a forum to read and post messages in, as well as a "chat" room of sorts and other interesting resources. I decided to try to be somewhat anonymous and so created an account under the name of AgeMeansNothing. YoungAtHeart was taken. :( I also created a corresponding YouTube account where I would post videos relating to Heeling. Check it out if you like.
So, with some research under my belt and some support when I needed it, I started practicing. Knowing I was liable to bust my butt in the process, I took it slowly, and carefully, making sure I got the feel for where my feet should be before I took a run at it. If you watch people on YouTube trying for the first time, the most common mistake is just trying to run into it. A lot of people assume that since you see little kids rolling around so effortlessly, that it's easy. Sorry, but it's not. Not by a long shot. Imagine a pair of rollerskates with the front wheels missing, or rollerblades with all but the back wheel missing, and you have Heelys. Sure, you can put your toes down a lot easier in Heelys than skates with missing wheels. Heelys wheels are also wide and flat, making it a little easier to maintain control than those other things would be, but that doesn't make them easy. Take a look at my first video, and remember, this is AFTER an hour or two of practice just pulling myself along with my feet "in the position."
So, I kept practicing as I was able to, and as time went by, I got better and better, enough that I could heel fairly reliably most of the time. I got this done just in time for Christmas when the boys would get their own Heelys. I was able to pass on my learning, and help them over the learning curve faster and more safely. Check out this video of them getting it down. Since then, we've heeled around at the Supermall, Pike Place Market, and even the cool skate park in Kent. We're no pros, but we have fun doing ramps and stuff. You never know what we'll be doing next!