Squeak
I imagine this is the crux of your argument.
“People die. People get sick. People have disabilities, physical and mental. People can be loners. People can abandon their community. People from outside a community can join. A community can impose harsher standards on certain people than on others”
We know the rate at which people die. We have a pretty good idea as to the rate they get sick. Granted Boys die, get (physically with mental illnesses women seem to have a higher incidence)sick and disabled at a faster rate than girls however at those ages the it is a marginal factor.
One can speculate on any number of theories however until without evidence it is simply speculation. I have spoken to a number of people to try to find out if boys become unmarrigable at a higher rate than girls due to undesirable behavior but I was not able to come up with anything.
When given the choice between a theory with a significant amount of evidence behind it, one whose mechanics you don’t seem to dispute, and speculation, I would go with the former.
Even if you are right that the reason for the disparity is something else reducing the age gap would alleviate the problem.
By the way the Avi Chai Day School study is in the publications section of their web site. The studies themselves are in pdfs in pop up windows which may be why you where not able to find it in a search.