These pants are between 3300 and 3000 years old, but they look like they could have been purchased in a parking lot outside a String Cheese Incident concert.
When I say these pants are the world's oldest, I should clarify that I mean "the oldest surviving pants we know of". Given the workmanship that's evident here, it's unlikely these pants sprang, fully formed, from the head of a nomadic herder in what is now Western China. Somebody (or, a lot of somebodies) had probably been making these garments for a while.
The pants were probably able to survive this long because their owner was buried in the Tarim Basin, a desert region that's known for producing natural mummies.