Fast is relative to the situation...
80 mile ride with 5000 ft of climbing with an 18mph avg and that is fast for me..
21.5 mile flat solo loop at 22mph and that is fast for me..
55 mile group ride with a 19.6 avg and that is faster for me because on the ride are some 28+mph runs and even some 30+ runs that leave me breathless or dropped...

I was averaging 16-17mph just a few years ago and thought I was fast... till some group blew by me..