I have a pretty good idea of what the real reason is behind society trying to stamp down on men who date younger women.

Basically what it comes down to is the fact that women 24 and older most likely have little interest in casual flings and are looking for a committed relationship, whereas women under 24 are usually still playing the field. Therefore, if a man past that age group is still looking to play the field, his options will be very limited unless he includes younger women in his dating pool. If this option is removed from the table, then that pretty much kills most opportunities that these men have to continue playing the field.

Notice that the age when society no longer considers women "too young" for older men corresponds with the age where women generally start looking to settle down: 24-25. I believe that if it became the norm for most women to continue seeking casual flings until they are in their 30s, society will start labeling women under 30 as adolescents and stigmatizing older men who pursue them.