I’m 68. I used to ride very hard and far, 40-50 miles were common. 10 years ago and according to my RWGPS records, so at age 60, was averaging 15-16 mph on solo rides. Last 2-3 years, distances have been down to 30-35 max, but that’s mostly as I just don’t do enough riding to work up to longer distances. My avg speeds are also 13 or so. Partially due to medical issues from 2014 on and harder to get over those issues, so that’s part of the reason not riding as hard. But age related decline is inevitable and you have to work very hard to overcome it.