《当你老了》是爱尔兰诗人威廉·巴特勒·叶芝于1893年创作的一首诗歌，原文如下：
```
When you are old and grey and full of sleep,
And nodding by the fire, take down this book,
And slowly read, and dream of the soft look
Your eyes had once, and of their shadows deep；
How many loved your moments of glad grace,
And loved your beauty with love false or true,
But one man loved the pilgrim soul in you,
And loved the sorrows of your changing face；
And bending down beside the glowing bars,
Murmur, a little sadly, how love fled
And paced upon the mountains overhead
And hid his face amid a crowd of stars.
```
这首诗是叶芝献给他的友人茅德·冈的，表达了他对茅德·冈热烈而真挚的爱情。诗中通过对老年人眼神的柔和和昔日影子的回忆，表达了诗人对逝去爱情的缅怀和对爱人灵魂深沉的爱。