eighteenth birthday 

When you become a legal adult and you can make your own decisions but your parents or any one older than you thinks you are still a child.

"It's her eighteenth birthday so she's going to get a tattoo."
"She thinks she's so grown because its her eighteenth birthday."

eighteenth birthday by Theimpracticaljokersarestilltr April 3, 2016

Eighteenth Birthday 

The age at which a girl is just old enough to have sex with an older man without him becoming a registered sex offender.

"Hey, its my eighteenth birthday! Now I can hook up with DILFS!"

Eighteenth Birthday by dilflover67 September 19, 2025