binahyeseira – I assume that you were addressing AZ, but I’ll disagree with what the goal is (he can speak for himself when he sees this).
I think the goal is to educate people that a 23 year old boy can be every bit as happy if he marries a 22, 23, or even 24 year old girl, as he might be if he married a 19 year old girl.
I know several couples who were in this category, (including my grandparents) and their marriages seem wonderful, B”H.
There are plenty of boys who are not choosy about the age of whom they marry (within reason), so why not try to set them up with a “slightly older” girl with almost no detriment! Often, in fact, a 22 year old girl carries (besides extra maturity) the benefit of having a better income, and despite the stereotypes, most yeshiva boys I know would rather not have to take much support from their in-laws.
As for those who prefer a younger wife, nobody is forcing them to marry or go out with anyone, and their are plenty of shadchanim (and always will be) who will gladly accommodate. The goal concerning this type of boy is to reduce how many of them there are, by removing the “stigma” of marrying an older or close-in-age girl. Anecdotally, there seems to have been some success in this area.
Where I may disagree with AZ is regarding boys going out earlier. I think the tendency in more recent years has been to start younger, often before they are actually ready, so I would think that a further push in that direction would be detrimental from a shalom bayis perspective, which is why I would prefer the gap be closed by encouraging shidduchim with older girls, rather than younger boys.
It is for this same reason (only much more so) that I consider the idea of polygamy to be a laughable solution (besides being illegal). Having marriages between members of different (even frum) cultures is similarly ill advised (this one has exceptions).