… through the worst storm in twenty years of Navy flying fading in the remote, intimate airways of his mind. (3)
This line seems to be a stylistic oddity in the story – it's more ornate and poetic than the language Thurber uses in the rest of the text.
"We've been all through that," she said, getting out of the car. "You're not a young man any longer." (4)
Mitty's age does seem to play a role in establishing his character. The characters he embodies in his fantasies don't show the same signs of aging (memory loss, loss of coordination) that Walter does.
Oh," said Mitty, handing the man the ignition key. The attendant vaulted into the car, backed it up with insolent skill, and put it where it belonged. (7)
Here, the narration slips under Mitty's influence – the word "insolent" is not objective; rather, it reflects Walter's state of mind.
"Any special brand, sir?" The greatest pistol shot in the world thought a moment. "It says 'Puppies Bark for It' on the box," said Walter Mitty. (11)
Walter's imaginary identity, in this passage, is strongly contrasted with identity in the real world.
'I was thinking," said Walter Mitty. "Does it ever occur to you that I am sometimes thinking?" She looked at him. "I'm going to take your temperature when I get you home," she said. (14)
Mrs. Mitty restricts Walter's potential.