18 when I left for college.
I tried to return for a bit after that, soon to be followed by a permanent break. About 35 years ago.
I don’t think it was possible for me to live with my parents any longer, and trying would have probably just hastened the split.
Conversely, I encourage people who have a cordial relationship with their parents (or even non-adversarial) to hang on for a while if it’s mutually agreeable and doesn’t hamper the child’s long-range plans. A couple of year head start, financially, can make all the difference today.