What is a good aveage speed for a mountain bike?

Question

ok flat level ground and age of 23 years old and road only

Answer 1

Depends on how much you want to pedal, your surface, and direction.

Answer 2

There is no "good speed" because speed varies upon terrain, age and the bike.

Answer 3

The answer to this kind of questions is always the same:

It depends.

It depends on you, your bicycle and the terrain.

In flat offroad I used to do 25km/h then 28km/h now 32km/h without problem for a couple hours.  I can peek and do short stretches of 40km/h

Now I am no rookie, but no pro either.

I have seen pros sustaining 40km/h+ in flat offroad for hours.

Answer 4

15 miles per hour is good