Marriages must be open to pro-creation and to unity in the Catholic Church. So since women can’t bear children past a certain age most people assume that this kind of marriage would not qualify as a Catholic one.
However, that is not the case. The word “open” is the key word in that sentence. Couples of any age that are unable to bear children are not trying to prevent pregnancy but rather they are simply unable to bear children for whatever reason (menopause or infertility). Their openness to the possibility of children however is still present in the sexual giving of the one to the other. Now that won’t produce a child as wishing can’t really change science, but there could be a miracle! God could choose to give them an unlikely child and that’s the possibility that the church asks them to remain open to. Should God give them a child the church asks that they accept that child with open arms despite the unlikeliness of it.