Here is the distribution of scores on AP stats from my class of last year, by gender:
Note that the mean is the same, but the variance is higher for males. There is some evidence, alluded to by the infamous Larry Summers, that such a pattern is true more generally. That is, men or more represented at the top and the bottom of distributions of ability.
My guess is that as of 1960, two things reduced the proportion of women in colleges. One was overt discrimination. A second was that much less than half of the population went to college, so that colleges selected more from the top of the distribution.
Leaving aside overt discrimination (although it really was an important factor), imagine that the rule in 1960 was for a college to accept everyone in my class who scored a 4 or better on the AP. Then 2 out of the three students would have been male. Suppose that today the rule is to accept everyone who scored a 3 or better on the AP. Then 5 out of 8 would be female.
My guess is that these numbers have really changed the mating game in college. When I was in college, girls could be choosy and a lot of guys wound up lonely. I think it's the other way around today.
Because social life is such an important issue for students, I wonder if they won't find a way to re-equilibrate the situation.