It depends on what type of job. I know Winn Dixie hires at 14, and many other places like Publix, McDonald's, Burger King etc. hires at 16. While a most other places you have to be 18, and some like...
You will briefly work for Tom Nook as a "part-time employee" when you first create your character. He will have you do several simple tasks (mostly focused on familiarizing yourself with the other...
There is a job market for welding jobs. I am not sure what location you are referring too, but my suggestion would be to contact an employment agency to find out where exact positions are.