I'm 52. I've been riding for the past 18 years. Last year I logged 3,300 miles. This year so far, 3.400 miles.
This past summer I road the Tour of Colorado. Check out the web site....
http://bicycletourcolo.com
My speed dipped an averager of about one mile per hour when compared to 12 years ago. Now I average 20 mph on a 28 mile route that's hilly. I live in Wisconsin and in my area there are short steeper hills. You'll need to break out of the saddle for quite a few of them. As you all know, the bike gets in your blood.
Now go have some bloody riding fun.