The fact there are no other interpretations that can be given to the two words other than the fact that a girl is a female child, the adolescent is still immature, or a young woman, while a woman is an adult female human.
While the above explanation is the most common meaning we have for the two words, regardless of the different societies that we have, there are other interpretations or meanings that people tend to have when using the two words. As I said, a girl is a female child, an adolescent who is still immature; however, this immaturity is not necessarily talking about the physical development of a female child, but also her mental capacity.
That is why a fully-grown person of female gender can still be called s girl because of her low mental and emotional capacity. However, a woman is considered to be a mature female human, both mentally and physically. Those who are above thirty years of age are usually called women.