I'm talking to myself here. I'm 58 and a n00b, having restarted riding my 2008 Trek 7100 late March. After a few weeks of riding 8-15 miles every few days, and a couple of 20-milers, I rode 34 miles in the Five Boro Bike Tour on May 2. It was hard, but it was a blast. The next day, brimming with enthusiasm, I signed up for the Montauk (metric) Century on May 16 and actually somehow completed it, feeling triumphant despite getting through it on brute force alone. (http://cihm.blogspot.com if you've got nothing but time on your hands.)
It's been 3 days and I'm still sore. I think I oughta back off for awhile and stick with 10-15 milers during the week and 20-25 once a weekend, until my conditioning matches my enthusiasm. I don't want it to stop being fun.
That's all. Thanks for letting me vent!