See figure 5 on page 148.
Menopause, on average, is reached at 51 years old.
But that doesn’t means that women can get pregnant until 51. 51 is an average, and it means that half of women get menopause before 51.
Half of women get menopause between 41 and 51.
Even worse, menopause doesn’t means fertility. It just means having menstruation. A menstruating woman can be infertile.
The average age of sterility is 41. Half of women turn infertile before 41 (between 31 and 41). The other half does on the next 10 years.
But there is also the problem of subfertility. Subfertility is a catastrophic drop in the capacity of having children.
The average woman suffers from subfertility at 31 years old. Half of women gets it between 21 to 31.
It means that to get the peak fertility of a woman, she has to be younger than 21. Up to 31, she has 50% chance (the toss of a coin) to have important difficulties getting pregnant, and if she waits up to 40, she has 50% chance of never being able to have a baby. Men marrying women older than 31 risk getting an infertile woman, and are guaranteed to have subfertility problems.
Those ages match the attractiveness of women: it peaks between 16 to 21, (she still looks like a teen), then goes down until 31, where women crash against the wall, and it fails catastrophically until 41.