From my readings on age and cycling the general trend line looks correct however the average speeds are grossly inaccurate (low) unless you are measuring neophyte speeds. For reference: At 67, my average speed this winter is 16 MPH with between 1000 to 2000’ of climbing. During the warm months my speed increases to 17.5 on average. In my 20s and early 30s, I could do a century at 20 MPH ave as a recreational cyclist.