This poem was written for Maud Goone for which he had a vey complicated relationship of unrequited love. In deep depression from the death of her two year old he wrote the poem.
She was an Irish revolutionary who ended up marrying another man despite many proposals from Yeats. He himself would go on to marry another, but many see ‘When You Are Old’ as a poem highlighting the failed relationship with Goone.
The poem is seen as one that is filled with love, but the last stanza is dark; the speaker is reminding his former mistress that their love did not last, and this is something she should regret for the rest of her life.
William Butler Yeats, widely considered one of the greatest poets of the English language, received the 1923 Nobel Prize for Literature.