When you get old, you can't talk to people because people snap at you. That's why you become deaf, so you won't be able to hear people talking to you that way That's why old people die, eventually. People talk to them that way.
This passage is one of Grandma's many characteristic epigrams on "old people," epigrams as long-winded and senile as they are insightful. As an old person, Grandma occupies a privileged position in Albee's cast, figuring as a character marginalized by and posed to comment ironically on the violent spectacle before her. The epigram is thematically significant as it points out speech's capacity for violence—that old people die because of the speech of others. Grandma's own absurd conversational behavior, for example, her apparent senility or deafness, is a form of protection against this violence.