I sold my first story when I was an undergraduate. I’d always liked to tell stories; in high school I started writing them down, and at age 19 I started submitting them.
I think it’s necessary for a successful writer to be a reader, but literature classes are if anything contraindicated for a writer. There are people who swear by writing classes/courses/groups, but my opinion is that at best they’ll teach you how to write a particular sort of story for which there isn’t a mass market.
I didn’t have a mentor, but I modeled my own work on the work of other writers whom I admired. I’ve wound up mentoring several writers who were already at a high level of skill and who were close friends. It’s not something I do for fun. I’m not any kind of teacher, and I’m uncomfortable even coming close to that role.
There’s no secret handshake. Writing is like playing basketball: it helps if you have talent, but even Michael Jordan practiced (practiced his butt
off).
And there’s nothing specially wonderful about being a writer/basketball player. No one need feel they’ve failed just because they’re not (at
core) willing to put in the enormous effort it requires to become good in either field.