I find that a lot of reports of cycling speed is much like golf scores (in reverse).
Since I live in Canada, I use metric measures.
20 km/hr is my average speed. I am slower uphill and a lot faster downhill, but I still average about 20 km/hr (i.e., 13 mph).
I have ridden with riders who were keeping pace with me and while my speedo said 20 km/h, theirs said 30 or more.
When people tell me they average 25 mph (40 km/h) or more on long distances, I just laugh.
My guess is that their speedo is not calibrated correctly (some are set for metric, but claim to be mph)
Or they are measuring a very short ride.
If you don't like your low numbers of mph, change to metric.