I have been tracking all of my cycling rides for years, and my data show steady drops in my annual average speeds for all rides. However, age is not the only reason why my speeds have dropped. About half of my mileage is from bike commuting, and my speeds are limited while commuting due to traffic, red lights, loads and riding solo with no drafting. I also have been riding more bike tours, included loaded tours, in recent years as well as riding on greenways on slower bikes with more gear. My average speed dropped a lot at age 58 because my daily commute distance increased from about 20 to 30 miles, and the past two years I have ridden substantial mileage on loaded tours and greenway rides at slower speeds.

So, I simply am not participating in nearly as many fast group rides that would increase my average speeds. When I do participate on group rides, my speeds are much higher, but the overall averages are driven down by the large number of rides from commuting, touring and greenways. That said, here are my annual average speeds by age. I typically ride 8,000-9,000+ miles/year, so the averages include a lot of data points.

Age - Avg mph

53 - 16.4
54 - 16.1
55 - 15.8
56 - 16.0
57 - 16.0
58 - 15.7
59 - 15.6
60 - 15.0
61 - 14.6

In conclusion, I have no doubt that my average speeds have decreased as I've gotten older. However, the drop in speed is not nearly as much as the data would suggest due to changes in the kinds of rides I do now compared to younger ages.