Until what age can a woman give birth?

Todays daf (Bava Basra 119) has a fascinating take on this. The Gemara states:

Rav Chisda taught that a woman that marries before age 20 will bear children until age 60. If she marries at 20, she will bear children until age 40. If she marries at 40, she will not bear children.

 There are a number of obvious problems with this:

1. What is the connection between getting married and the ability to give birth at a later age? Getting married before 20 does not magically push off menopause until the age of 60.
2. No woman can give birth through natural means until the age of 60
3. There are plenty of women who get married at 40+ and have children naturally

This is another case where the Gemara contradicts reality as we know it today.