The Squire is the Knight's son, accompanying him on this pilgrimage. We think he's a pretty good squire; after all, Chaucer tells us that he rides a horse well, can joust well, and he carves the meat for the Knight well at dinner. After the Franklin interrupts his tale, he praises the Squire for being everything a young man ought to be.
From his portrait, we end with the impression that the Squire is a teenager