At the age of 60, my round trip rides (6-9 miles both ways) are consistently averaging 12-13 mph (with a relatively large hill now). On the commute with the aforementioned hill, it is up to 35 mph down, and 4 mph up. Trading the relatively flat areas of North Decatur to Clarkston, GA. for the hills of Stone Mountain/Tucker/Lilburn convergence didn't seem to make a difference for my average.