| Quote #1
Under the October twilight the water
The emphasis on October and "twilight" suggests an ending. The speaker talks about this time of year and day both because it was probably when he observed the swans, but also because it is convenient: he too is entering the latter half of his life.
| Quote #2
I have looked upon those brilliant creatures,
A word like "sore" makes us think of how our body gets sorer as we get older. The speaker implies that we might also start to feel sadder, feel more "sore" emotionally in addition to physically. This is a somewhat negative view, for it implies that old age brings a form of heartache.
| Quote #3
All's changed since I, hearing at twilight,
The phrase "lighter tread" suggests youth, a carefree attitude—basically anything that isn't old age. The absence of a "lighter tread" at the moment of the poem's composition suggests that the speaker has become wiser, but less carefree, and more of an adult.