The speaker notices, with a mix of calm and surprise, that they are visibly getting older. The poem doesn't dwell on grief. Instead it reaches for plain, slightly odd comparisons. Aging is like a worn shoe, something used and creased by time. Then it becomes "a picture of a picture / of a picture," a copy of a copy, each version a little fainter than the last. That image suggests how a person can feel thinned out or blurred as the years pass.
The final two stanzas move outdoors. The speaker walks alone at dusk, pacing "up and down," which suggests restlessness or quiet reflection. Dusk also hints at a life moving toward its evening. The ending is the most striking part: a hill suddenly appears "at the door." Perhaps old age feels like an obstacle that has crept up unnoticed, something to climb. The mood is quiet, solitary and wry, with a small jolt of wonder at the end.