I can only speak from personal experience. My wife is actually very close to me in age (close enough to make AZ proud) but I did have dates who were over four years younger than me.
A little background first. I was a guinea pig at a new high school which was off to a good start. I was one of the first graduating classes and everyone in my class and above (to the best of my knowledge) is shomer Torah Umitzvos. A very unfortunate incident happened about 18 months after I graduated (and left) and the young Hanhallah, who were not prepared for an incident like this, took actions that made the situation much worse. The Yeshiva developed a horrible reputation from which they never recovered and eventually closed down because of it.
While dating I began to notice that the older the girl the bigger the chance was that they wouldn’t agree to go out with me because of the high school that I attended.
(They told the shadchan that all of their married friend are married to guys who went to “normal” high schools or that none of the other guys they went out with went to “strange” high schools. Some shadchanim asked me if they should tell the girl that while I was there the yeshiva had a respected reputation but I felt that if they are not making a decision based on where I was for the past six years, but where I was for the four years before that, than I’m not interested in them.)
Younger girls, on the other hand, who have fewer married friends and dated less people were not as likely to say no based on that reason. I gave up dating girls that were that much younger because I felt I couldn’t relate to them as well.
Again this was just my personal experience.