Boy is the term used to describe young males, typically below the age of 17. However, the boundary between "boy" and "man" in't always clear. 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.................................Some Boy, some Man
20+.................................Man unless he’s grossly immature or really cute
Another way of seeing it
0-2 Infant 2-4 Toddler 4-7 Little kid 7-10 Older kid 10-12 Preteen 13-19 Teenager 20-35 young Adult 35-50 Middle Aged 50-70 Older man, sometimes senior 70+ Senior/elderly
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 means he’s immature and should grow up.
