for me, this song is about longing for the innocence of childhood. It reminds me of the poem, "the boy and the man" by ee cummings.

I don't think that Tom meant 'the good old world' litteraly, but more in the sense of seeing childhood and adulthood as two different worlds.

"When I was a boy, the moon was a pearl the sun a yellow gold.
But when I was a man, the wind blew cold the hills were upside down."
here he is comparing both worlds, and obviously childhood is the prefered one. i can kind of feel the longing for what was, in those lines.

"But now that I have gone from here there's no place I'd rather be
than to float my chances on the tide Back in the good old world."
I think that part means that he would take his chances and do about anything to get back to 'the good old world.'

"On October's last I'll fly back home rolling down winding way.
Scare crows are all dressed in rags out at the edge of the field I lay
and all I've got's a pocket full of flowers on my grave."
This part reminds me of death, and maybe that he's hoping that once he dies that there won't be heaven or hell, but 'the good old world' of childhood.

"Oh but summer is gone I remember it best
Back in the good old world."
the ending part I cant place my finger on, I think it may be that he realizes that his childhood is gone and that theres no way of getting it back; and maybe the only thing he can do now is remember the way things used to be.

I think it's quite a sad song. sad, but still lovely.