I am almost 66 and have only been biking for two years. I ride 100+ miles every week, mostly for physical conditioning. I weighted 240 when I started. Now weigh 194. Not exacly a lightweight, but a heckuvalot better that it was!
I have never ridden in a group becasue I am afraid I will not be able to keep up and I don't know exactly how to ride safely with a group. I average about 15-17 MPH on rides of up to 50 miles.
Group riding sounds like fun. I probably should just give it a try and stay on the rear of the pack if possible.

Wayne