UBI: if you didn’t understand the simply relevance of what i wrote then i don’t think there’s any hope for you to grasp the issue and thus i fully understand why you don’t grasp the significance of age gap.
here it is one more time in a nutshell.
Age gap is only a problem if the number of children (girls) in 9th grade, is significantly fewer than the number of children (boys) in 12th grade.
the determining factor of how significant that discrepency is will be how many children are born each year. otherwise known as increase in birth rate also able to be measured by children per family.
B”H our communities are having many more children per year and there are more children being born per family overall, now than was being born then, thus 30 years ago the number of boys in 12th grade was very close to the number of girls in 9th grade because 30 years ago the the community was NOT having 4% more babies each year than the year previously.
WHAT CHANGED IS a 4% increase in children born per year, this didn’t exist 30 years ago.
B”H (because more children being born is a bracha of course) it is now happening, and thus the difference of girls in 9th grade to boys in 12th grade is very stark.
If this isn’t clear enough, then i give up trying to explain it to you.
I just realized your post earlier. The answer is 2. in other words, 30 years ago there was far less year to year growth.