a guy i was texting said he was 18 . I have heard he is 13 and he says he will report me. I know i have been stupid and as i am gay things could look bad. What can i do IF he reports me
If you have never met him, just play dumb i.e you were just flirting with him thinking he was someone else. There is nothing the authorites can do, depending on the content of the texts.
You stopped once you knew his age, so it was a genuine mistake, suggest you take more care in future.
if there are any threats, including the one he's made re reporting you, contact the police. You've been an innocent pawn in this little darling's game.