What is it we wanna doooo..
Now that I'm allowed to be in love with you?

from The Roots (Ft. Patrick Stump) – Birthday Girl Lyrics on Rap Genius

Meaning

Now that the girl is of age, the man is legally allowed to have sex with her, which he’s probably been waiting for her for quite some time.

Although, in most cases, a big age difference is still really creepy.

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