But if we could keep shifting it to younger and then to even younger girls instead of accepting that the older girls are continually left out
If I understand you correctly, you’ve hit upon an important point. “Shifting to younger and younger”, if you mean that the younger girls remain (temporarily) single, means, in effect, focusing attention on the older girls, and trying to get them married first. If I am not mistaken, this is precisely what NASI tries to do (and gets it over the head for it).
There’s another solution proposed by those who “get it”, that age gap is the cause of the lopsidedness (gender disparity). Some are trying to have boys get married younger ( I think NASI has encouraged this as well). This is indeed more of a long term solution, but will not help those girls who have already passed a certain age.