"'Ponce de Leon was looking for the fountain of youth'"
I feel like this quote really helps to illustrate Ruby's character. She's really denying the fact that she's getting older, and the stairs represent her aging. The farther up she goes, the harder it is for her to move and the less she can deny to herself that she will end up like all other human beings. It is not just that she doesn't want to have a baby; she doesn't want to die. She watched her mother growing "deader" with each child she had, and she doesn't want to be like that. Like Ponce de Leon, she wants to stay young forever and avoid the responsibility of having to raise a child. However, we all get older, and whether or not we actually have children, none of us can avoid the passage of time and the toll it takes on us physically and emotionally. One way or another, we're going to have to accept the responsibility of what we've done in our lives. As soon as we accept it and stop trying to move on and ignore it like Ruby does by the end of the story, we will have "plenty of time" (79) to mentally prepare ourselves for the next step in our lives.