bk613: “I would imagine all the Rabbonim who signed the various Kol Koreah encouraging boys to date at 21 are opposed to them dating at 18.”
That’s an assumption (or as you put it yourself, your “imagination”) and a wrong one at that. The current standard in the hamon hoam is 22-23. By encouraging 21 they’re seeking to encourage younger marriages in a manner that they feel the hamon hoam might listen. If they encourage an immediate jump from 23 to 18 they know they’ll be ignored.
But that doesn’t demonstrate they oppose 18. I note you’ve still failed to answer the simple question of naming *any* Litvish Gedolim that are on the record as opposing marriage at 18.
There are none.
But maybe you know better than Chazal.
Philosopher: The glut of extra Chasidishe boys can marry the glut of extra Litvishe girls. This trend is also happening somewhat and has picked up over the last decade or more.
Leiby and KlugerYid: Excellent comments.