48. I find most commuters around here (edit: in the burbs, city folk commuters are a lot younger) are over 35, with a peak in the mid 40's to 50's. Exactly the age group that suddenly discovers that if they don't do something about fitness now, it will be too late. I think that a desire for fitness and/or a love of cycling make a commuter. Otherwise, its too damn easy to hop in the car. In my 20's and 30's, I dabbled in cycling commuting but always found an excuse, and had other ways to keep fit. It wasn't until a demanding career collided with having a family that fitness deteriorated, and I had to find a way to work exercise into life. Cycle commuting is great for this, since it converts lost time (driving) into exercise time, and time is a hard thing to come by.