The definition of a teenager.

Officially sanctioned definition:

teen·​ag·​er (ˈtēn-ˌā-jər) - someone who is between 13 and 19 years old

Actual definition:

teen·​ag·​er (ˈtēn-ˌā-jər) - a made up construct that just delays maturity for young adults by another 7 years.