@Dominions Son
The difference between women and girls has everything to do with age, and nothing to do with being sexually active.
I would tend to mostly agree. However, the actual differing factor could originally been marriage status.
In Latvian (a living relic of a language possibly calling close to the roots of proto-indo-european) any woman can only be meita = "daughter", sieva = "wife" or mΔte = "mother" and nothing else, derivatives of those excluding no other word to refer to a human female generally (you always could by profession, role or trait since every noun and adjective is gendered).
Godess is always "mother"; spinster, servant and prostitute are "daughter" regardless of age, but while "wife" is the most neutral term that almost completely map to general concept of "woman" it necessarily implies adulthood, while the modern politcorrect derived term sieviete technically doesn't. Funny enough, meitene the modern world for "girl" is derived from "daughter" as derisive diminutive, and has swallowed the meaning "girlfriend" whole.
Therefore to me, a girl can be of any age or sexual activity, but she's unmarried and thus a dependent and potentially sexually available, while a woman is assumed to be someone's wife and thus perceived as independent equal.