What is the theme in The Sound of the Mountain by Yasunari Kawabata?

Aging is the main theme of the story. The main character of this novel is Ogata Shingo, a man in his early sixties who one day discovers that his memory is not what it once was. Shingo begins to think he might be coming close to the end of his days, especially when he comes to realize that many of his friends are already dead. One night Shingo believes he hears the sound of the mountain, a sound that suggests to him impending death.