I've been in the trucking deal since 1972. 5,000,000 miles. That's enough that I don't have anything else to prove.
Last fall I was at the shop that was doing my block and head work. I casually mentioned that if I could turn back time I'd trade all those miles for a shot at learning machine work.
The foreman damn near hired me on the spot!
I'd do it in a heart beat but a 72 year old guy with three implants and five herniated discs doesn't have much of a future in a new career.
When I get back to my 60 hour per week part time driving job I have time to decide when I want to retire again.
Maybe when the house is paid off in three years.
I'll sell my two race cars and buy a two door post B body.
To the OP... Go ask one of those shops for a job. Every machine shop I know of is willing to train the right guy and you are still a young guy.