Maggie,

I rode a Trek Hibrid for about 2 months before I got my road bike and I never road more than 30 minutes...then I got stuck on a longer ride on my road bike and was shocked that I could do it. Seems it takes me about 30 minutes to warm up on a bike. Every time I ride I spend the first 30 thinking it's just a bad day and I'm not going to have a good ride, then the next thing you know I've been riding an hour!!

I'm not saying go for it yet - you know your body and your fitness level better than anyone - just thought I'd share.