They are not "train drivers." They are engineers. Up in the cab they are paired with a fireman, who was the stoker before automatic feeding of fuel to the firebox.

They were employed by the railroad. That is, Union Pacific has one batch of drivers and Southern Pacific had another.

Now, in most primitive times, the engineer was just that -the designer and engineer behind the one-off engine. Then they were mechanics experienced in handling steam engines (either stationary industrial or those on steamboats) hired and trained by the expanding rr.

Once the industry developed, your career path began as a young man joining the rr. You would work in the engine houses and get promoted to jobs along the line like switchman or work with repair crews. Your real step up was getting to be a brakeman, which was part of the running crew. Eventually you might make it to fireman on a minor line, then go up in prestige of trains. Ah, the glorious day in middle age when you made it to engineer of some little local!

If you look at pix of Victorian engineers, they are usually grey or white haired. You knew your equip't and routes, knew where the bumps were and how to handle each curve. You were proven reliable and level-headed.

No, you wouldn't be a youngster walking in and asking to go to train driver school. ;-)