I moved out when I was 18 and went to college. No parental support or full-time job needed. All these things vary by location and living situation, time, culture, etc. This was the mid-late 90s. I went to a local college w/ academic scholarship, plus Pell Grant and freshman Stafford loan- that pretty much paid my rent for a year. I split a 4 BR house 3-ways. I worked full-time in the summer at a restaurant, and saved my money. Roommates worked part-time in retail/restaurants as did most people I knew. Since this was mid-90s, we had 1 computer on dialup in the house. I think we skipped cable. Basic landline w/ an answering machine. We all had cars we owned outright, from working/saving or modest gift from parents.
Even though times have changed- tuition has increased (but so has minimum wage), “necessities” have evolved, I’m pretty sure I could do the same thing today in today’s dollars, and I know people who do. My brother and sister never lived at home once they left for college, either.
As far as getting “established” goes, there is a not insignificant % of the population (millions) that never really establish themselves in a stable well-paying career track, yet still manage to not live with their parents. They get jobs, roommates, don’t buy a bunch of consumer goods or intoxicants while mooching off relatives, etc.
When I was 22, I had a really bad break up. I had made a deal w/ my GF to transfer schools to be closer to the school where she was pursuing her doctorate. After I moved I got really depressed, went into a prolonged state of depersonalization, and dropped out of school.
All it took was one summer back living on my mom’s couch (we didn’t have a mansion) for me to save up enough money to get my next apartment and never look back. I never made more than single digits pr-hour, either.
Culture, and changes, has a lot to do with it. Maybe the moving out at 18 thing was just more expected and desired in the past than it is now. I don’t know anyone who actually WANTED to live with their parents at 18. Even my friend who was a virgin until he was 26-27 at least wanted the option to have a date spend the night if he ever got the chance. Plus whatever other reasons you can imagine that young adults don’t wan’t to live with their middle-aged/elderly relatives. Now it might be different.