Author here. I worked at internships and smaller contracts in HS and college. But I've been coding since the start of highschool with coding competitions and jobs that helped my neighbors and my grandparents. Even in retrospect, even though they were small or not as full time as what I did now, I would still count them as learning career experience

And I have been hired somewhere else. I was really close just to quit early and go to contract work. But I got really lucky with an offer a few months ago. If someone's feels like they want to quit, definitely investigate the amount of work it will take to be self employed. It's a lot, but understanding your own skills and being able to market that is a great ability to learn!