Thank you for using Just Answer.While every state has different laws, so it should not be assumed that the adult would be in trouble, mistake of age is historically not accepted as a defense. This is because many crimes, such as statutory rape
, are considered to be "strict liability" crimes. Strict liability requires no guilty mind, but merely the act itself is enough to get you into trouble. Speeding, for example, is a strict liability "crime." You don't have to think about speeding or have the pretense to go faster then allowed - the moment you exceed the speed limit, you are guilty. Similarly, if a girl tells someone she is 18 or 20, or whatever, and it turns out to be false and then have sexual relations, that person cannot in many states later claim "Well, she lied!" The act itself can make it criminal
. That said, merely talking to a minor in a chat room or online/over email isn't a crime. However, when there is an exchange of pictures, sharing of pornographic images, etc., that is what can lead to criminal charges. It may not be fair to an adult (and I would agree to an extent it can lead to people being unfairly criminalized) but that is why most attorneys would advise people to never chat online with people they don't personally know, because even in an "adults only" forum, there is no way to prove a person's age.