Do you ever go urban with your mountain bike? Nice long rides where you can get comfortable on the bike without worrying about roots or rocks and you can ride for as long a time as you can stand and build up from there? Urban riding isn't quite the same as mountain biking and I'd personally rather crash in the woods but it is nice for building a fitness base and spending the time necessary for getting used to the way your bike handles, maybe even popping over things that are very familiar to you such as very low (at first) curbs or riding off a low (at first) step or two. Riding with a group of other people below, at and just above your skill level also helps too. It is easier to relax and just ride if you don't feel you're the one holding things up, no matter how nice your riding companion is about it.
Two years, schmoo years. It takes what it takes.

Ride. Lots. Sing a few jaunty tunes while you're at it.

Really.