Love
At its heart, "When You Are Old" is a love poem, expressing the speaker's unending admiration and affection for the addressee. The speaker's love is defined by his ability to see past the obviously positive and charming elements of his lover's appearance and personality. He praises her for being undeniably beautiful, likable, and gracious. However, he emphasizes, those obviously lovable traits are not the ones to which he feels most attached. Instead, he loves above all her "pilgrim soul," a phrase suggesting adventurousness as well as a certain dissatisfied or roving nature. He also describes his love for the "shadows deep" of her eyes, and for the "sorrows of [her] changing face," both of which evoke not only physical beauty but also sadness. The speaker's love, it is implied, is distinct and special because it is non-superficial and multifaceted.
Memory
Yeats plays with time and memory in complex ways within the poem. First, he projects forward, imagining a future in which his lover is old and the two of them are parted. He then imagines, or instructs, his lover to reminisce about their past. That reminiscence, in the hypothetical scenario described by Yeats, is actually brought on by the lover's perusal of the poem itself. In other words, the writer is composing a poem in the present, and intending that poem to be used to reminisce about the past in the far-off future. The dizzying complexity of this timeline suggests that, to the speaker, the paired acts of reminiscing about the past and looking toward the future are displays of love. His love extends to the older version of his lover, who now exists only in his imagination—meanwhile, he imagines, her love will extend back through time, to the younger version of him that she can access only in memory.
The Passage of Time
A theme inextricable from memory, in this work, is that of time and aging. The poem's two characters continue to love one another as they age, but their love ages with them, becoming more subdued and thoughtful. The imagined future version of the lover, as described in the poem, is not young and passionate but instead old and nostalgic. When she thinks about the loss of her love, she experiences sadness, but at a distance and with the perspective of old age—she speaks of him "a little sadly," with an emotion that has become softened over the years. This altered orientation is treated ambivalently by Yeats. On the one hand, he presents this muffling of emotional intensity as something of a loss, but on the other hand, he stresses the additional perspective, maturity, and empathy that comes with aging.
