so you want the age gap should be even larger? (if the girls start dating earlier)
girls will start dating earlier, giving them more time to date, before they become the "old crop".
The way it is now, girls get back from seminary b4 the summer, a lot of the new boys don't want to go out till after the freezer, so the "new girls" are held back from dating till tu bishvat, the next crop of 1000's of girls come back from seminary few months later, so basically each "new girl" only gets few months so to speak to date while they are in their "prime", before the become "old news" and get looked over by the new girls...