Painted Girls

The English word girl first appeared during the Middle Ages between 1250 and 1300 CE and came from the Anglo-Saxon words gerle (also spelled girle or gurle). The Anglo-Saxon word gerela meaning dress or clothing item also seems to have been used as a metonym in some sense.
Girl has meant any young unmarried woman since about 1530. Its first noted meaning for sweetheart is 1648. The earliest known appearance of girl-friend is in 1892 and girl next door, meant as a teenaged female or young woman with a kind of wholesome appeal, dates only to 1961.
• Usage for adults
The word girl is sometimes used to refer to an adult female. This usage may be considered derogatory or disrespectful in professional or other formal contexts, just as the term boy can be considered disparaging when applied to an adult man. Hence, this usage is often deprecative. It can also be used deprecatively when used to discriminate against children ("you're just a girl").