I had a bad bike-crash when I was 12 years old...and didn't touch a bike again until I was 31. My brother convinced me to try a race (mtb) three months later...it was a blast and I made many of my best friends through bike-racing.

So...if we all can do it, you can too!

What type of race do you plan to enter? That will, in part determine some of your training. 25 miles for a mountain bike race would be considered fairly long and you would really need to train for endurance. For a road race, that's on the short side. If it's a crit you will really really need to hunker down and work on your pack skills and cornering if you are "rusty". If it's a time trial you'll want to practice getting in your aerobars and train by heart-rate.

If you already own the Airdyne....great! If not you may be better off getting a trainer (lots of threads on those on this board!) and usuing the bike you plan to race.

Good luck