Gotta start somewhere
#1-Yes you are in shape to do a race. Most races have a first timer category or a beginner 1 category which is for people like yourself. It really isn't about you vs other riders it's about you vs you
#2- On your local single track pick a specific loop. Ride it as best you can
-write down your time
-average mph
-max speed
#3 Now you have a baseline. This is your target. Ride hard, ride for fun, rest, then go beat your baseline. This becomes your new PR....Repeat
#4- Get addicted to racing, and mtbing. Then start learning more. Ride with some more experienced riders or clubs, Read these forums and the archives. Get some books: Ned Overend, Performance Mtbing, Mountain Bike skills from
www.leelikesbikes.com, some training books like Single Track Mind. Learn how to drink and eat right for riding.
#5- Continue for many many years