I’m faster in a group than solo, and slower in the hills. I’m quicker when trained and rested ‘on form’. And I’m quicker when skinnier. Some rides are purposefully hard, while others purposefully easy. As such, my speed varies so much that I haven’t a clue what average is. Honestly, I don't even look at it, unless it's a Strava segment or something (and even then it's for benchmarking purposes).
“It doesn’t get any easier, you just get faster” – Greg Lemond