“Notably, Chang’s report claims that biological females develop earlier than males do, so requiring girls to enter school at younger ages will create classes in which the two sexes are of more equal maturity as they age. This, the author posits, makes it more likely that those classmates will be attracted to each other, and marry and have children further down the line.”
(…)
“The report does not include evidence of any correlation between female students’ early enrollment and the success rate of their romantic relationships with men. The author also does not detail specific mechanisms by which his proposed policy would increase romantic attraction or birthrates.”
Look at long term trends, it’s not a 30 years thing, 100 years ago Finland was getting close to being under minimum required to renew its population.
When women get rights, people get education and people have access to birth control, they stop having kids, the situation in the world at the moment only adds more reasons but even in a perfect world people wouldn’t have enough kids to renew the population.