Either 18, 19, or 22, depending how you define it.
I went to University at 18, but parents still helped out with finances. 19 was the first summer I didn't live with my parents (I was with my sister), but my mom was quite distraught over this (I'm the youngest, so I'll always be the baby), so I spent the next two summers at my parents house. Yeah, my mom was a bit clingy, but living at home was cheap and I do like my family.
After graduation I never moved back in my parents. In fact, I never moved back to their town. Almost 10 years later and they're all (parents and siblings) asking when I'm moving "home".