Dating Equation?

I learned something new last night. Apparently guys have an equation for the youngest age they can date. Who knew? It goes something like this...
(Age of Guy/2)+ 7 = Youngest Age of a Girl They Can Date
So a 21-year-old guy could date a girl as young as 17. Yeah, I'm sure that will go over well with her mother.
But, I was also told that if its a number that isn't easily divided by 2, then you have to round up the age, because girls are more mature than boys. I would totally have to agree with that statement (haha).
Did anyone else know about this? Because this was all news to me...
I'm sure this is a super lame post, but I'm totally over it :D