Well I got into BDSM when in was in my late teens, i'm now in my late 20's

I would say that it depends on your location, many of the local munches mid 20's tends to be the average for some reason, yet at other events later 20 to mid 40s is the average.

It all depends on various things, so I don't think any one age catagory is right, since I've known it to vary from event to event.