You fucking weirdos are the worst. Age of consent means they can legally have sex with OTHER MINORS. It doesn't mean a grown-ass adult can fuck a kid.
age of consent means anyone of that age and up can have sex as long as it's consensual. that does include people over the age of 18.
in some places there's a limit, so if you're over that age it's not applied to you(for example, if the limit is 5 years, then you can't be 25 and fucking a 14yo). in pretty much every country, the law states that it's not consensual if the older person is in a position that holds power over the minor(like a teacher).
pretty normal in europe for someone who's already 20 to date someone that's still in highschool, because age of consent here is usually 14 or 16.
it's only against the law if the state he's in has an age of consent higher than her age, then it's considered statutory rape.
for example, when kylie jenner was dating that older dude, since they live in california, where age of consent is 18, they couldn't have sex without him getting in trouble with the law. and at the time it was all eyes on them. there was actually lots of controversy when they travelled alone to places like new york, where the age of consent is 17, and iirc went to paris together, where the age of consent is 15. they purposefully exited california so they could fuck without breaking the law