Boy

Boy is the term used to describe young males, typically below the age of17. However, the boundary between "boy" and "man" is blurry. If he's had complete sex he's more likely to be a man.

Boy...Man
If he’s immature or antisocial he’s more likely to be a boy or a yob.

Age...............................Term

1-5...................................Boy

6-10..................................Boy

11-15.................................Boy

16-20.................................Mostly Boy, some Man

20-25.................................Man unless he’s grossly immature

Boy...girl
Calling a young female a girl can sometimes be a complement as it suggests that she’s young, virginal and attractive. Calling a young male over 17 a boy is always an insult as it suggests he’s immature and should grow up.