An interesting point, but i think that “shidduch crisis being less severe (if that is, in fact, true, but let’s say it is) and couples getting married younger in communities that have stricter separation of the genders” is correlational, not at all causational…i.e., stricter separation of the genders does not lead to more marriage and younger marriage. That is a function of the communal standard more so than anything else. And of course i’m not claiming that a tall mechitza at a wedding 100% prevents two people from talking (although the OP apparently would like it to), but it’s more representative of the attitude…ceiling high-mechitzot, and, for that matter, long sleeves, are not things that even the most religious Jews ever did in Europe. It’s a post-war invention, as the world in general and the Jewish community in particular, shifts waaaay to the right, and are just…excessive, and not halachik. Heck, a mechitzah in shul only has to be 40 t’fachim, but today we have floor to ceiling cages with either zero visibility or one-way glass. It’s just not the way things were.