Mazal- the gedolim are not telling boys to marry younger. That is just NASI. If they make it seem like gedolim are the ones who think boys should marry younger then they are using a very liberal creative license (to put it mildly).
The age gap theory is wrong. No reputable (or unreputable) statistician stands behind it and it makes little sense as an explanation of the recent explosion of the crisis or the proportions. NASI is irresponsible and dangerous for misleading and manipulating frum families into acting against their own best interests.