Lied about age in online relationship

OK NOW THAT I GOT YOUR ATTENTION I NEED HELP BECAUSE HONESTLY I DONT KNOW WHAT TO TELL MY FRIEND ANYMORE SHE DOESNT LISTEN TO ANYTHING I TRY TO SAY BECAUSE SHE SAYS "I DONT UNDERSTAND" SO HELP ME UNDERSTAND PLEASE

So my friend F(17) lied about her age on this streaming app to this one person, she didn't say anything about her age but she said she was in college. The guy she lied to her age about is a cool guy, I honestly don't know much about him because I've only seen him once while they were on a collab stream but I guess he took an interest to her and has been also been acting sweet and flirty with her recently? So that's where the problem comes in. My friend talked to me about it yesterday and she was giddy and stuff but I raised up the concern that it's not good if he has a different perception of her age bc in the long run when he finds out he might get mad and she might feel heartbroken, because I really feel like his attitude is getting to her and they might enter a relationship sooner or later. But anyways. Yeah. If you have any experiences in lying about your age online to friends/partners please share them and what happened after they found out/you revealed it because I'm so stressed out for this girl I'm genuinely concerned because I've also seen things like this before and UGHHH I just don't want her to make the wrong decisions. Please help thank you. Feel free to give me advice to tell her too please, I really don't have any experiences regarding this so I'm pretty clueless and have a biased opinion on online relationships in general