The basic argument here seems to be that because of population growth, there are more 20 year olds then 23 year olds. Therefore, if boys date at 23 and are only marrying the 20 year olds the extra 20 year old girls will be left out. This only makes sense if you assume that all girls are getting married at 20 and all boys at 23. In reality, those may be only the average ages. Meaning, that some boys will not get married right away at 23. Some will not marry a girl 3+ years younger than him. The suggested solution here is to force people to marry their own age. This is not going to practically work. The real solution as the popular speaker suggested is to remove the stigma, to suggest shidduchim between people closer in age, to teach boys that they don’t have to marry someone much younger than them. If boys would listen to all shidduch suggestions equally and not first look at the younger ones, then the problem might go away. Someone used the line earlier “there are not enough boys”. Of course there are enough, only one is necessary. The trick is finding that one. It’s all in Hashem’s hands. Hashem decrees who everyone will marry and it’s just a matter of finding that one person (and realizing that the person might not have every quality that you think you deserve/need).
As for segulas: daven sincerely, work on your bitachon, do your proper hishtadlus.