Straightforward: my 29-year-old son is dating a 16-year-old girl he met at a jazz festival this summer. Openly. He had a same age long-term girlfriend until last year, when they broke up amicably. We really loved her, she was basically our daughter-in-law and we’re still in touch. His current girlfriend’s parents know about their relationship & are cool with it. For the record: it’s also legal in our country. We don’t think it’s right though, he’s a grown ass man while she’s a high schooler. He’s also very successful professionally, handsome, takes good care of himself, has a good personality, etc. so it’s not like he’s lacking options. He just says he likes her - that’s his why. He’s not a bad person, I know that, but still this whole situation has changed our perception of him quite a bit. We’re having a rough time to say the least.
Well, have you tried asking him why he picked her? Note my choice of words here. Specifically don’t ask him why he didn’t pick someone else but what he likes about her. My personal guesses (!) are: they share an interest in jazz music, they had a good time together at the festival and she doesn’t expect him to act like society imagines “an adult”: she lets him make up for something he missed when he was younger.
About her being hurt: he’s your son, you know him better than we do. Do you think he’s the kind of guy who would do that? If not, look out for signs that it might actually be happening instead of relying on your expectations. Stay in contact with her parents. At the same time, make sure she’s comfortable talking to you. That way you will know if something happens. But please don’t accuse either of them of something that isn’t actually happening.