The speaker in sonnet 73 compares himself to yellowed leaves, ruined church buildings, twilight, sunset and a last glowing ember lying in the ashes of a fire that is almost burned out. All of these reflect aging, an end. For example, the line "When yellow leaves, or none, or few, do hang/ Upon those boughs" which "shake in the cold" indicates that the warm days of youth, symbolized by spring and summer, are ending, and winter, meaning old age, is coming soon. "Bare ruined choirs" are the ruins of an old church that once was young and vibrant, while "twilight" and "sunset" are classic images of old age. When the speaker mentions "the ashes of his youth," he conjures an image of his young days being burnt out and dead, for ashes are a symbol of death. He is mourning lost youth, using melancholy and bittersweet images of aging.