Not sure why my last post didn’t make it.
The avi chai studies are posted in their web site
There are a number of ways to estimate the growth rate of the yeshivish community. There have been studies done in EY that put the growth rate at close to 5% although a portion of that is probably due to “Immigration”.
One can also count the average number of children per family and extrapolate the growth rate from there using some readily available formulas. The difficulty as with many population studies is defining the community. The more narrowly it is defined the higher the growth rate.
DD
As you can see from the site I posted above the total death rate for White boys is about 132 per 100,000 before age 24. The rate for girls below age 20 is about 600. This is quite a distance from the 5% needed to eliminate the birthrate disparity.
I am not saying this is the only cause of the problem. It may be that more boys go off the derech to the point they cannot marry into the community. However at this point this is simply a theory without evidence. Even if this where the cause the problem would still be ameliorated by reducing the age gap.
squeak
Noone want the age gap to be the issue. It is an extremely painful issue and yes it is demoralizing. But unless we recognize it it is only going to get worse.
To this point other than offering what is IMHO a rather speculative alternate theory, you have not in any way addressed the fundamentals of the issue.