"The Man Who Was Almost a Man" ends with some good old-fashioned train hopping. All aboard!
After the whole Jenny ordeal, Dave is feeling pretty unhappy. He got his gun, just like he wanted, but everyone still treats him like he belongs at the kiddie table. Plus, he now owes Hawkins fifty bucks—which is over two years of wages. Things went from bad to worse in the blink of an eye.
Ironically, this makes Dave feel more like a man. He shoots off his last remaining bullets—and this time, "the gun [is] still in his hands" (209) after he fires. Dave's increased skill represents his growing maturity: He might not be a man yet, but he's taken the first step in the right direction.
Then, of course, he hops onto a moving train, eager to find "somewhere [...] where he could be a man" (212). Dave has realized for the first time that his life at home is a dead end. He can do one of two things with this knowledge: stay and accept his fate, or run away in the hope of finding somewhere better. While there are plenty of ways it could go wrong, his decision to bounce represents Dave taking control of his life for the first time—it represents him acting like a man for the first time.