Two year rule 

It is socially acceptable to go out with anyone within the two year age bracket. However the younger of the couple should be at least 14.

The "two year rule" means a 14 year old girl can go out with a 16 year old boy and still being socially accepted.

Two year rule by randommzz October 20, 2009

Two year rule 

If you're between the age of 12-16, it is socially acceptable to be in a relationship with someone 2 years or so older or younger than you

Man, isn't she a bit young?
Nah bro remember the two year rule!

Two year rule by yoitsgavin May 12, 2013