How old people are called adolescent, youngster and young adult.
How the differences are they?I mean I'd like to know what ages of kids(teens) are called as each of them.

Question

How old people are called adolescent, youngster and young adult. 
How the differences are they?I mean I'd like to know what ages of kids(teens) are called as each of them.

Answer

An adolescent is usually between 12 and 18 years of age. A young adult is usually between 18 and 30 years of age. A youngster is a child under 12. Youth is considered to be between 12 and 30.

Answer

monica is perfect!

Answer

Usually we say "the adults" but if the person is really old "the elderly"