I started MTB at 44years old (a couple of years ago) so I understand what you mean about learning these new skills.
Firstly, it helps if you know somebody who can drag you around and give you a few tips. DH did that for me, but there is a limit to what you can learn from your spouse before you kill them!
I also bought a magazine that had useful tips and a free DVD with some skills stuff on it. That was useful to get some theory going.
But by far the best thing I did was take a lesson (or three) with a local skills coach who runs classes just for girls. He took you through the basics (because you can learn all this great stuff from others and books, dvds etc but still be doing something a little bit off - like posture - that renders it all a bit useless) and then you practised over a broad range of obstacles and he'd spot you so you built confidence. The best thing he ever taught me was that you can get over nearly anything if you just "look ahead and pedal."
I think as an old roadie rider, I found the obstacle thing quite worrisome, and tended to look right under my front wheel at the rock or root I was just about to hit up. It took a long time for me to re-set my gaze to the "down the road" view I have used on the roadie. This is something you really need to aim for. You can't do a damn thing about the root that is three inches from your front wheel (other than fall over it) but if you "look ahead and pedal" you'll probably find that you roll over it easily! And besides, there may be something a lot bigger down the road that you need a bit of time to gear up (or down) and prepare for!
Persevere - it is a ton of fun!
PS: I find I am always willing to go over bigger and more interesting obstacles if I am riding in a group and everybody in front of me just flies over them without thinking!