We can reduce the age gap, meaning it will be less of an issue, and more women will be able to get married. But it could never be eliminated (without the unrealistic scenarios or reinstitution of polygamy) and there will always be an oversupply of girls.
I don’t think that is completely accurate. Ideally the system would self correct so that if one year the age gap was tilted one way, the next year it would tilt back. This would be accomplished if all age bias was eliminated.
Meaning, if everyone would marry suitable people regardless of age (withing the basic range), then if there were more older girls one year, there would simply be more older girls marrying that year.