I don’t know what the training curve is, but years ago when I was just out of college and working in my first career job, there was an older guy in our office who also had the same dream. He wasn’t exactly happy or cut-out for driving a desk so he abruptly quit one day to join the railroad with the goal of being an engineer. Within the same year, he called another guy at the office and said meet me by the tracks at a specific intersection to say hi. This was in Winona, MN – a big railroad town where trains often came to a complete halt to wait-out other trains switching tracks, etc. Sure enough, the train stopped and my old co-worker apparently leaned out the window of the locomotive and he and my other co-worker they drank coffee and BS’d for about 15 minutes before they had to get back underway. He was loving life. This was within a year of him quitting, I have to think he was definitely in-training and not running solo, but he made his dream happen and fairly quickly.
The only thing about today is that I think autonomous trains are becoming more-and-more common. Not sure if they still need personnel on-board for specific duties or systems, but it may be a dying profession. Perhaps someone else knows more.