On many places in the world this is considered acceptable. Up to 150y ago it was mostly ok everywhere. Also social class counts sometimes.

No, I do not condone that a 16yo (whatever the gender) has a love relationship with a 42yo. Its so much wrong on ALL aspects.

But without knowing the background, location, family situation and much more, giving out judgment is just stupid.

I am father of a similar teenager, who luckly has no such tastes, but I do not know what I would do in such a situation. Would I condone it? Absolutely not. Would I prohibit it? Mmmmm would that be of any use? How would I address such an issue is probably by talking to both (separately). Yes I would go as far as telling the 42yo to fuck off or I would call the police on him/her. Or destroy his/her car/mess him/her up personally if I am in a place where the police would just do nothing.

But I cannot judge how and why the parents in OP post, without knowing more of the situation.