It totally depends on the situation and the society.
In the US I think it should be when one has, more or less, completed their education.
I moved out when I was 19, when I graduated high school.
I had the choice to go directly to college or leave, I left.
There was no great turmoil and I am very close to my parents. If anything I had too ideal a childhood and needed to learn life on my own.
I could have changed my mind had I wanted to.
I think it is a bad thing for children who don’t carry themselves to be allowed to remain in the home after they have reached an age where they could support themselves.
In many cultures children stay well into adulthood and only leave when they have families of their own. In a fare number of cultures several generations live in a home and children, usually the women, only leave when they are absorbed by another family.