Age Rule

The rule (invented by wise men but which should also be adopted by wise women) which states that half your age plus seven is the youngest acceptable age of a potential romantic partner. (Does not work inverted.)

Example: "C'mon, man, she's legal!"
"She's 19; you're 26. Just because she's not jailbait anymore doesn't mean you should date the girl. Don't you know the Age Rule?"
Number Example: 26/2=13. 13+7=20.