In general, "proud livery" means fancy clothes that are beautiful and showy. It has a more specific meaning, too. The servants of a nobleman during the Renaissance would wear livery, which was a uniform that told the world who they served. So livery are clothes, but clothes that tell a story.
- Line 3: "proud livery" (line 3) is another metaphor for the beauty of the young man. His good looks are like a beautiful costume that is admired ("gazed on") by everyone around him.
- Line 4: Here's the other side of this extended metaphor. If a young man's face is like "proud livery" then an old man's face is like the oldest, crummiest clothes you can imagine. In Shakespeare's language, those old, worn-out looks become "a tattered weed" (line 4) that no one cares about. There's probably a bit of a double meaning here too. We get an image of a brown, worn-out plant in winter, a dead weed. At the same time, weed was a common term for a piece of clothing in Shakespeare's time. This pun is a good example of how Shakespeare can make one word do a lot of work.