Growing up in the 70s I rode my Schwinn 10 speed everywhere and never had an ounce of fat and I could eat anything I wanted.
Quit riding when I turned 18 and put on weight ever since. Blew out my left knee so I cannot walk at the age of 45. Still wanted to be mobile so I started to ride again. Purchase Specialized Rockhopper for trail and Allez Double for road.
Went from 240lbs to 180lbs over a 6-8 month period. Found out that you could loose your gallbladder if you loose that fat (after the fact.) The bright side is I lost another pound or so due to the surgery.
Age 46, my longest ride straight is 65 miles. I hope to do a 100 mile trip before the end of 2010. I dont use my Mountain bike except when family goes hiking. Eventually I will need to get this knee replaced but thanks to my bikes I am putting it off until I turn 80 ;-)

Forth Worth TX. Great place to ride!