DR. Pepper:
It seems like you do agree with the math, (quite a haskama from the math expert that you clearly are). The question you are addressing is the reason WHY boys (or if they do) prefer younger girls.
That being so, if you suggest that it is a unchangeable social fact and therefore it is a waste of time and energy to attempt to encourage more close in age shidduchim-so be it. I for one have come to realize that the stakes are high, way to high to simply give up because its to hard to change.
The Rabbonim and Roshei Yeshiva behind the movement to encourage more close in age shidduchim are banking on the idea that although there may be boys that will insist (for whatever reason) on only dating/marrying significantly younger girls; there are PLENTY of boys that would be and (the past two years have proven) are willing to date close in age. NO one is claiming that there should never be a 19 year old girls marrying a 23 year old boy. What is clearly needed is more- many more close in age shidduchim. The past couple of years have shown that simply raising awareness has changed many attidutes.
The next step is to institute some kind of MINOR structural change that would result in a scenario where boys and girls entered the dating pool slightly closer than what is occurring at present. If such was to occur besides the obvious mathmatical benefit, the specific social concern you raised would also be alleviated.