Started riding a bicycle

Over the years I've ridden 10 speed bicycle's for exersize but haven't kept it up having several bikes in non operational condition...broken, hasn't helped either!
So I recently purchased a used Mountain Bike from a shop in Hilo thinking I'd like to start getting in shape again since I have all this new found energy. I rode my new/used bike home and was greeted with none of the usual side affects of out of breath, leg cramping fun that follows the "first" ride. Since then I've increased my distance daily and can feel my leg muscles getting stronger without the next day pain. I'm up to 6 miles a ride now and will continue to increase the distance, we'll see in a year how it goes.
Mahalo for reading, Mark