Really? Eleven is not that unusual. I was 11 and it was 1970. Now nine would be awful young.
that was 50 years ago, and by evolutionary standards insignificant. But the recent decades may have introduced phenomenon that directly affects the biological growth of young individuals; i.e., vaccinations, technology, “pandemics”, etc. The current trends may be an indication of instinctual survival where the physiological potential for procreation occurs on shorter cycles.