I wonder if it is even possible to eliminate the age gap in a society where men choose which woman they will marry. After all, you’ll need to convince most men to choose to marry a somewhat older woman when they have the ability to choose a younger woman.
As opposed to a society where, for the most part, someone other than the couple choose who will marry who. Like by the Chasidim.
So the Litvaks are going to be stuck with the age gap, and its consequences, unless they virtually fully adopt the Chasidish dating/marriage model.
Klal Yisroel used to virtually across the board follow what’s today known as the Chasidish dating/marriage model until about a hundred or so years ago. In fact, almost all goyim did as well. The switch to the love/marriage/choose-your-own-girl model got us stuck with the age gap.