Along about the time Eisenhower became president I started taking my .22 rifle apart. Some years later my father, wondering if I would ever amount to anything, asked me if I might want to go to gunsmithing school. Even before Clint said it, I had some idea of my limitations and didn't think I was a businessman at heart. Amen. Eventually I got into law enforcement and so made my living with guns, in a way of speaking.
Along the way I got to know some pretty good gunsmiths, both full time and amateur, and learned from them. Took some armorer's courses, and worked on quite a few clunker guns. It's been fun, and I still putz around. Sometimes I want to claim Brownell's as a dependent.
The comments above are dead on, and echo exactly what was being said thirty and forty years earlier. If anything, things are tougher than they used to be and machinery more expensive. My son went from a kid nuts about airplanes to a 6000 hour plus pilot with ratings up the gazoo. Expensive as it was, I suspect it was cheaper than getting up and running as a gunsmith. And he gets to be outside more, has some choice about where he lives and goes, and sometimes gets paid well for it. Oh, and don't forget benefits. It helps a lot to have a wife working who can provide them.
That said, I love working on guns. For 99%+ of us it's best done as a great hobby while we keep our day jobs.