Siri's voice had grown even more beautiful with age. There is a fullness and calmness there which can come only from knowing pain. (6.436)
This is one of the few benefits of growing old that the novel illustrates, even if it is coupled with the fact that with old age comes pain and suffering. At least that's not all. There's also "fullness" and "calmness." Uh, we're pretty sure we'd still take youth.