Dear Roberta,
Thank you for your questions. While I must confess that I need to spend some more time reviewing the questions and answers on this site, I would be surprised to find an answer suggesting that if one or both spouses-to-be were infertile, they would not be able to marry. This is certainly not the case in the Catholic Church, and I am pretty sure it also is not the case with civil marriage. In any case, one does not necessarily need to be fertile to marry validly. As you so correctly pointed out, if fertility were a requirement for valid marriage, an elderly man and woman would not be able to marry.
However, it is true that the Catholic Church, in her treatment of the Sacrament of Marriage in the Code of Canon Law (church law), does consider “antecedent and perpetual impotence, whether on the part of the man or of the woman” to be an impediment to valid marriage(see Canon 1084). If the man and woman are not able to consummate the marriage, the marriage should not take place. This is based on the teaching of Jesus in the bible, when he refers to Genesis 1:27 and 2:24 in Matthew 19:5-6a: “Have you not read that the creator from the beginning made them male and female and that he said: this is why a man must leave father and mother, and cling to his wife, and the two become one body? They are no longer two, therefore, but one body.”
Regarding virginal marriage, there have been cases in the history of the saints, where spouses, after having consummated the marriage, and indeed, had children and raised a family, have entered into a mutual agreement to live celibately. However, this agreement to live as brother and sister was only carried out after having lived a valid sacramental marriage for some time. This arrangement, when prompted and affirmed by the Holy Spirit, is completely legitimate.
May God bless you.
Fr. Blaise Berg