I can comment on the first 3 lines of your post -- the ones that WERE on-topic.
I understand infertility, marrying late, etc. but that doesn't explain why 999 out of 1000 Baby Boomers have 3 or 4 children. Usually not less than 3, but usually not more than 4.
It's up there with "own your own home", "debt is no big deal", "invest in the stock market", "increase your standard of living over the years", "vacations are important" and "use credit cards" in the Baby Boomer Rule of Life handbook.
Let's dredge up my qualifications again -- I've been a trad for 3 decades. I've seen many chapels and known plenty of trads. I seldom meet large families founded by Baby Boomers. Even the "good ones" used NFP, or didn't grasp the whole CULTURAL Catholicism (as taught by the SSPX, etc.) until much later in life.
Heck, a few Baby Boomers have smaller families because of the modern epidemic of C-sections. "Trust the doctors", "Trust pharmaceuticals/pharmaceutical companies" are also tenets of Baby Boomers.
Incidentally, every tenet I listed above as being held by Baby Boomers -- I completely reject myself. Except for owning your own home, but even then I differ from them. I believe homes should NOT be paid on for 30 years. Mortgages should NOT be a fact of life.