The speaker overhears two friends casually talking about their mothers, both eighty and still around. Their ease sets off a quiet calculation in him: his own mother, if she were alive, would be eighty-three. Everyone in the conversation is about the same age, but only he has lost his mother.
What follows is a wish that feels both tender and a little impossible. He imagines she had married younger and he had been born earlier, so they might have shared "a bit more time." The poem then turns on an honest, uncomfortable admission. He now wishes she were alive, yet there were moments when she was, and he wished otherwise. That contradiction is the heart of the poem.
The ending is direct self-reproach. He calls his past attitude "regrettably foolish" and reflects on how easily we neglect those who care for us most. The mood is subdued and reflective, with grief sharpened by guilt. The plain, conversational language makes the regret feel real rather than dramatic.