Auto Erotic

A policeman passes a parking lot around midnight and notices a couple in a parked car. He stops to investigate and sees a man in the driver's seat and a young lady in the backseat, quietly reading a magazine.
The officer knocks on the window and asks whats going on.
"Listening to music," the guy says.
Pointing toward the lady in the backseat, the officer asks, "And what's she doing?"
"Reading a magazine, of course."
"How old are you?" asks the officer.
"I'm 28."
"And how old is she?"
The guy looks at his watch and says, "Well in 11 minutes she'll be 18."