How far can you drive an average 50cc scooter?

Most scooters (depending on engine size) get 75-100+ MPG, most 50ccs are in the 100+ range.
Now 'How FAR can you drive' depends on the size of the fuel tank, a 50cc scooter with a 50 gal. fuel tank would not be recommended but could go 500+ miles. (a direfully terrorful ride on a 50 with a 50 gal. tank).
Now if you asking about long term usage most 50s need maintenace on a regular basis, so more maintence means a longer life span.

until your bum goes numb

Until you run out of gas.

Given normal maintenance, about 50,000 miles.

Depends how many hills there are and how steep. If there is one right out your front gate then you might get around 200meters.

...until the world runs out of hydrocarbons.

As far as the road goes.