Answer:
The average age of the women was around 40 years old,
However, a lot of women died during child birth, in fact, before birth the women made other care arrangements for their children in case they did die.
-----
Just as an informal study, I looked at the ages at which about 20 medieval women died. The women who lived through early childhood tended to die at an age over 50, but the infant mortality was quite high and brought the life expectancy at birth down below 25. All these women were noble, and information on other classes is hard to get, unless we go pouring through village registers. I am sure there are studies that have been professionally done, but I have not been able to find any to cite.