To be honest, it would seem a bit 'creepy', especially if an older man said this to a girl under 18. The word 'woman' can be used from 18 onwards. There's also a phase from 18 to maybe early twenties when either 'girl' or 'woman' can be used, depending on the situation and perspective of the speaker.

'Girl' can actually be used for any female at any age - sometimes as a compliment if someone says you are youthful looking. A girl can also be referred as a female child, a school child, a daughter. We tend to use 'young woman' or 'young lady' once the female has reached a certain maturity from the age of 14 years old - so as not to make them feel a primary school child but a young teenager. At 14 girls enjoy putting on make-up, buying clothes, dancing, singing, chatting and socialising with their friends. I can also use the term 'young lady' or 'young woman' if I was cross with a teenage girl - sometimes the mother or teacher will use this. All the other comments from the others stand too.

i think Girl: refers to the female human starting from the moment of the mother’s pregnancy. Until childhood and teenage years. women: is the term given for female humans who have reached the maturity period and adulthood commonly around 18 years old and above. if i'm wrong please correct me Natives :)

"Girl" is a general term that can be used to refer to a woman of any age. "Woman" usually implies that the girl is over 18, or more mature. I agree with another commenter that if someone, especially a man, referred to a girl under 18 as a "very special woman", that would seem a bit creepy. A more subtle way of using woman would be to refer to a girl as a "young woman." To make it simple: Girl - under 18, Woman - 18 or older

As I know, woman is for female 18 and above, and girl for female 18 and below :)