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.
Oh, don’t get me wrong. It is a bit weird and concerning. But weird and concerning alone are not enough to stop something that’s legal and at least for now seems to work pretty well. And like you said, not much they can do about it. The best course of action is to deal with it, be as accepting and supportive as they can and be prepared to help if things do go wrong. Everything else will make things worse.