Mathematically the only way you could ever eliminate the age gap so that you have enough potential grooms for every unmarried woman, is if either a) every shidduch is between a boy and girl of exactly the same age or b) the average age gap of shidduchim is zero – meaning an equal number of older boys marry younger girls as the number of older girls marry younger boys (by average age.)
Barring one of those two scenerios, you will always have an age gap that results in not enough boys for all the girls to get married. This is true even if the average age gap is reduced to one or two years.
This is the hard and sad mathematics of this. And I don’t see either scenario as realistic. 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.