What an encouraging thread. Seriously. I just came across this forum whilst searching for MMA forums, and went straight to the training and nutrition section. I saw this thread... and couldn't pass it up.
I'm in a very similar boat. I'm 6'0", 225lbs, and... well... a month shy of 22. All the same, in spite of the fact that people are shocked to hear my weight (I have a rather dense frame, so the weight doesn't make me look like a human-shaped jello dish), I've got some fat to burn. I've never been good at exercise for its own sake, so I started considering martial arts.
Which led me to signing up for a summer BJJ class offered by the local community college while I wait for University to pick back up. At first, I wasn't thoroughly excited about the class (or BJJ), but now... I'm hooked.
I don't plan on going UFC, but I'm glad to hear that it's possible for a guy like me to get into shape and get to a point where competing is possible on more amateur circuits. That's cool stuff.
Anyway, I just wanted to post a "me too" comment. I'm glad I'm not the only one wanting to get into the sport this late in life (wow... 21/22 is now late in life?).