According to a local radio station in Atlanta.....
Older person's age divided by 2, add 7 years. If the other person is younger than that, it's just weird.
So, lets say you were a 30 yr old man, a druggie, and possibly a felon, without a job, and you were dating an 18 year old girl, living at home with her parents. According to the above, that would be icky. (30 divided by 2 = 15 plus 7 = 22) Just sayin'.