Speed depends SO much on so many factors, such as age, weight, condition, bike type and weight, temperature, hydration, gears, terrain, experience, weather, blah blah blah...
so much so that I believe to compare speeds between people is almost meaningless.
The right speed is what's right for you.
I average about 10mph. I'm an 56yr old cyclist with no athletic background on fairly hilly terrain with a loaded steel bike, and I ride for health and enjoyment. Works for me!