19.1 is a respectable average moving speed - you're definitely a strong rider.
Above 17-18mph the air resistance dramatically influences things, and even elite racers might average 22-23mph on solo training rides (faster in groups).

Well done!

I haven't used a computer in many years - since I stopped racing - but I tend to ride pretty hard on my commutes, gauging how I feel day to day in a given gear. Some days I feel like I am effortlessly spinning the same gear that I struggled to stay in the day before.