I'm 55 and have ridden a bike most of my life, but mostly for commuting and recreation- roughly 3-5000 road miles a year plus some small fraction of that on MTB trails. Almost all my road riding is urban or suburban in character with substantial hills. My actual average for a ride is around 11-13mph due to climbing and traffic lights. I'm in good shape since I'm a runner, but am too small to be a fast cyclist- someone else could probably have a faster average in my riding conditions.