Just a quick addendum, even though I know this is old.
There are state laws called Romeo and Juliet Laws. Basically, they grant leeway so a 16-year-old having sex with a 15-year-old, for instance, is not rape. These laws vary by state and not all have them.
But the law is unlikely to be enforced in these cases anyway. Simply put, prosecutors are much more interested in going after child molestors than stupid teenagers.
"I don't believe in magic. But I do believe in interpreting coincidence exactly the way you want to." -Sherman Alexie