I've long had a strong position on the question of whether young Dati-Leumi boys should marry during their years of Yeshivah study. I strongly believe that marrying while in Hesder Yeshivah is a bad idea, and bad for marriages.
My belief is based on my own observations and anecdotes from friends. Basically my position is that one's life style and beliefs in yeshivah are not a good indication for your future life. People change dramatically when they leave yeshivah and go to university, and even the best of us see a dramatic change in our religious observance.
The normal dating age for Israeli Yeshivah boys is 22-23 – basically when they return from army service. What I've seen happen time and time again is that these boys marry relatively frummy girls – who think they are marrying a Yeshivish type of guy. However a year or two down the line, when the husband in no longer surrounded 24/7 by religious study and religious men, they are shocked to discover that these boys are not really as frum as they would like. This is often a disastrous recipe for young married couples.
This is why I've always advised young boys in Yeshivah not to get married until after they have finished a year or two outside of the framework.