The "yellow wood" could also mean early spring, no? Echoing in my mind is another poem by Frost, "Nothing God Can Stay":
Nature's first green is gold,
Her hardest hue to hold.
Her early leaf's a flower;
But only so an hour.
Then leaf subsides to leaf.
So Eden sank to grief,
So dawn goes down to day.
Nothing gold can stay.
In "The Road Not Taken," the leaves trodden underfoot would be there in any season, not just autumn, since it is in a forest.
I had always thought the story was about a critical choice made during one's youth, with the road evidently symbolising one's life and the fork in the road, a moment of decision. The lines "I shall be telling this with a sigh, Somewhere ages and ages hence" implies the speaker is middle-aged and not yet old, with some time yet to go within an ordinary lifespan.
However, the first answer posted here makes sense, too, and I must reconsider my initial interpretation of the poem. Ambiguity, I suppose, is part of the beauty of poetical expression!