Is it weird for a 27 year old to be with a 19 year old?

My cousin is 19 & she’s talking to a man who is 27 & they’ve had sex. I’m concerned about it. The man should be able to get with someone closer to his age. Plus my cousin is very “ditzy” & a bit immature but she’s absolutely beautiful. I don’t want her to get hurt!!! But I don’t want to hurt our relationship by me telling her she needs to find someone else.

The other guy she’s talking to is 26 about to be 27... I don’t know why they want someone so young?! Is it weird or is this normal and okay?