Moved out at 18, I started college at 17, so moved out for my second year at the local college.
I worked during undergrad (30 hours/week as a waitress at a coffee shop) and received Soc Security survivors benefits (my father was deceased.)
Mind you, this was the 70's, a time when wages were higher and cost of living was lower - it was pretty normal to move out at that age. We also had lower expectations too though - I shared a house with 4 other students, ate a lot of rice and beans, didn't buy fast food or eat out, couldn't afford to buy a calculator until grad school (used my trusty circular slide rule), drove a used Pinto, etc.
At the time, I never considered staying home (even though I might have been able to save up some money by doing so?). I had two younger siblings and no privacy for my sex life. But mostly, I just wanted to be independent.
Now I have one son living with me, working similar type job and hours, but he would never be able to afford to move out on his own on his income. The minimum wage is a disgrace these days.