On his birthday, the speaker looks into a glass of red wine and sees his own reflection staring back. The sight bothers him. The poem's central trick is a pair of opposites: he describes himself as "infirm as a child born yesterday," weak and helpless like a newborn, yet the wine he sees himself in is "red and old." Birth and age end up in the same picture.
The title suggests a celebration, but the mood is quieter and more uneasy than festive. The word "vexed" tells us he is irritated, even unsettled, by what he sees. Judging by the imagery, he feels that growing old brings him full circle, back to a kind of frailty that resembles infancy. The wine adds another layer. Wine is supposed to improve with age, but here its oldness seems to mirror his own, and the dark red reflection gives him no comfort. The poem is short, but it leaves a wry, slightly rueful feeling about time passing.