modernmax wrote:
Both < age of consent = fine
Both > age of consent = fine
One is > age of consent, the other is < age of consent = not fine.
I don't see why this is such a difficult concept to grasp.
That's an oversimplification.
The exact rules vary by location.
In Texas, the age of consent is 17 and it is illegal to have sex with someone under 14 regardless of your age. If one of the two is between 14, 15, or 16, an age difference of 3 years is acceptable. So 16 and 18 would be okay even though they are on opposite sides of the age of consent. If both are over the age of consent, then age doesn't matter. If one of the two is under the age of consent, there is something called "indecency with a child" that covers a variety of things including sex, sexual touching, exposing onself, ... .
And, of course, if the couple is married to each other then the limits above don't matter. In the mid 1970s, there was one married couple living in the town in which the husband was 26 and the wife was 14. Nobody really knew what to think about that.