Since becoming reacquainted with the poem a couple of decades on from 8th grade English, I've read it as regret at the way age reduces your choices. That comes

Since becoming reacquainted with the poem a couple of decades on from 8th grade English, I've read it as regret at the way age reduces your choices. That comes from interpreting the fall woods as being the autumn of the narrator's life, and focusing on "Yet knowing how way leads on to way, I doubted if I should ever come back." That is, when you're young, you can choose one path and presume you can come back and take the other path sometime; you've got lots of time. When you're getting old, a lot of choices are more or less the only shot you will get; you cannot count on having the time to come back and try the other path.