I spent last year doing the whole spinning thing, but it was one where you brought your bike and trainer into the gym for a good 2 and a half hour 'group ride'. When we finally hit the road for a real group ride I found that I could beat the people who were whupping me in the class. Bike handling skills and years of road riding can make up for the age/fitness differential that are not accounted for when stationary.
This year I just bit the bullet and rode in the freezing cold but when it got below zero I would supplement with some time on the trainer.