The average US worker has a salary of $46,800 (in 2018) before taxes. Assuming they saved everything and spent nothing, it would take over 5 years for them to make 250k. Again, this is before taxes, and without spending anything. For the vast majority of people, 250k is a lot of money.

Assuming they saved everything and spent nothing, the average worker would have to work the entire length of all human history in order to earn a billion dollars. If they were to make as much money as Jeff Bezos, they would have to work for 2.8 million years.

Assuming you earned a million dollars every year, it would take 1000 years to earn your first billion dollars.

It's not possible to become a billionaire simply through working, as humans do not live that long.