Asa_Jim answered your question. If the other person is a minor and you are legally an adult, any exchange of sexual/explicit photos or other material or conversation is a crime. If a 17 yo claims they are 19, looks 19, shows you an ID/DL that claims they are 19, it does not matter, you are an adult having improper interaction with a minor and can face criminal charges where your lack of knowledge of their true age is irrelevant.

