
Unique laws wasn't the reason why Khadijah (ra) was able to have children so late. People in those times were fitter healthier and aged later, with women reaching menopause well into their late 50's maybe later. My mother tells me that women reaching menopause in their 30's and 40's was virtually unheard of in Pakistan, although due to people increasingly following a modern lifestyle this maybe changing. I also learnt from the accounts of a writer who was a police officer in the Indian army (before partition), that the normal height for women was around 6ft tall and diseases was rare.
It is only due to unhealthy lifestyles, environmental pollution, toxins from chemicals, drugs, furniture, dyes, processed foods etc that the health of humans is suffering. Thus what maybe a scientific fact today, can't be applied to similar matters of times gone by.