I think there should be a word for when a woman reaches the age at which her mother birthed her. Some ideas:
Mumday. Momage. Maternal return. Materological age. Matriarchable. (omg please help.)
To be that age is to live in a palindrome, time folded in half, where stories are told backwards and forwards from the same starting point.
But if we could come up with a word for it, it would mean more than just an age. It would mean an experience which is that you have to get to the middle to start understanding the beginning.