az, one thing i do know. in order to accomplish encouraging young men to marry younger, it will have to be done in conjunction with encouraging young women to marry younger. you can’t encourage young men to marry at 18 (or 20 – whatever the young age may be), while on the other hand encourage young women to do otherwise. it is important for both genders to marry young for many reasons. (not the least of which, is if an 18 or 20 year old young man is going to get married, he will likely be marrying a young woman of between 17 and 20 years old.)
the way to implement this encouragement, is through chinuch. parents, melamdim, rabbeim, morahs, melamdos, roshei yeshiva, rebbes, and rabbonim should encourage and instill in everyone the importance of marrying young. and this kind of education should begin from a young age, for both boys and girls.
popa, it was done for thousands of years in europe, and only in recent history, primarily america, did marrying later become the norm. i don’t see why we cant successfully revert to our tradition of so long.