Lines 13-20 Summary

Get out the microscope, because we’re going through this poem line-by-line.

a little bored, a little old and strange.

Well, he feels a little bored, old and strange (though we're guessing you already deduced that).
This guy is pretty aware, not just of his surroundings but of himself. We mean, how often do you stop and say to yourself, "Hey, I feel a little bored, and a little old"?
Unless you're on a plane that is. Shmoop always feels bored, old, and very, very strange on planes. Maybe it's all that recycled air.

I remember, as a dreamy
backyard kind of kid,
tilting up my head to watch
those planes engrave the sky

Our speaker remembers looking up, as a kid, at planes just like this one, flying overhead.
There's something powerful about that word "engrave." It gives a sense of importance, and permanence. Normally you'd engrave something on a ring, or in stone, and it would be there to stay.
This business of flying seemed like such a noble, serious business to our speaker when he was a kid, so much so that he uses that word, engrave, figuratively to describe how the planes streak across the sky.
Yet our speaker, now an adult, seems bored and distracted when he's actually on the plane he used to daydream about.
And that image, of a tiny tot looking up a the sky once again highlights the distances we have going on in this poem. To this kid, those planes way up in the sky must have looked absolutely teeny. But to the adult in the plane, the backyard in which that kid is standing isn't even visible.
He's already jumped from his view out the window, to his neighbor, to his emotions, to Muzak and his seat cushion, to his oddness, and now he's going back to a memory from childhood. This is a speaker who likes to cover a lot of ground.

in lines so steady and so straight
they implied the enormous concentration
of good men,

The kid version of our speaker was impressed by the steadiness of the planes flying overhead. He thought the pilots must be very focused, very good men.
This reminds us a little of that image of those Kansas farms. The straight lines and orderliness were also seen in those square fields of wheat and corn.
Our speaker seems to be telling us that he used to think there was something essentially good about such orderliness and control. But does he now?