Here are some numbers from me just to compare. I'm 57 and have been riding for about 8 years.
My Max HR is 194. My average on a typical ride is around 150. For a 10 mile Time Trial the average is around 175.
My average speed on a solo 60 mile ride with 4000 ft of climbing is around 17-18 mph. I've done 100-160 mile rides with less than 4000 ft of climbing and averaged 21-22 mph (with a group).
My average speed for a 10 mile Time Trial on a flat course is 26+ mph.
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Ride your Ride!!