I am 42 y.o and went on my first group ride today. When I showed up, I was surprised to see 50% of the riders were 50+. Further, a number of the riders were 60+ (I'm guessing). Now, I figured I was in decent shape, running 15 miles and riding 50 miles a week. I'm thinking that I'll just hang back with these guys and not be a show off. To make a long story short, in our 40 mile ride, I was surprised, inspired and certainly respectful of many of the 50+ riders who beat my up a 1,600 ft (in about 4 miles) climb. It was really great. I hope I can be in such good shape 10 and 20 years from now.
Here In Seattle, the Cascade club rides, a ton of the rides,the ride leader is well over 50+. They even have a category called "brisk" which I have not ventured into as I know I won't be able to keep up.