How long constitutes a beginner mountain biker? When I first started in April I sucked. But know, a few months and a new bike later I've improving on every ride. I've been log hopping, bridge jumping and taking on tougher and longer rides. It really feels good to be making progress. Things are starting to come togethor now. I can ride 15-20 miles at a good pace no problem. Man, winter is gonna suck when I can't ride as much.