If were to ask a woman they would tell you that your still a kid till your mid 40's
Edit: Since I've been called out as sexist, I should note that I apply this equally to women. I've likewise met 40-year-old girls and 17-year-old women, and the difference between them is the same: The capability to earn a stable income and take responsibility for themselves and others.
Sometimes being part of a partnership means you focus on internal rather than external roles: Supporting the family instead of earning an income. Who does what is then negotiable within the family, and that's OK.
We call women, with no stable income but devotes her life to her household, women. We don’t call them girls because ‘they don’t have a stable income’.