Q. 1. Can a Sacramental marriage be valid when seniors get married? Surely, they cannot be open to procreation because of their age.
A. 1. To answer your question, it is necessary for you to understand what it means to be "open to procreation."
"To be open to procreation" means to believe and accept the possibility of a miracle. It is to believe and accept that God could choose to give a child to a senior person. This remote possibility is what the Catholic Church ask seniors to believe in. Should God give them a child, the Church asks that they accept that child with open arms despite the unlikeliness of it. Anything is possible with God.
Once this openness to procreation is present among seniors, they can enjoy a valid Sacramental marriage.