In "An Acre of Grass," the speaker, an old man, rails and rages against aging. Rather than being desirable, his mere acre of land shows the elderly speaker's sense of being limited and hemmed in by his age. He notes that his body is weakening and that he is alone at night in his house, with only a mouse for company, but that is not the person he wants to be.
The speaker fights against being diminished by age. He knows it is a temptation simply to become "quiet" and capitulate to death. Nevertheless, that is not the "truth" inside him.
Instead, he yearns for more than to totter around peacefully on an acre of grass. He wants to experience an old man's "frenzy." He states that he wishes to resemble old men in literature who raged against their age and infirmity. Like King Lear, for example, the speaker wants to run into a storm madly, fighting all the powers ranged against him and crying out to express the same angry notes as the thunderstorm.
He also wishes to be like historical figures such as Michelangelo and William Blake, who fought old age. He wants to "shake the dead in their shrouds." His soul still swells with a sense of power, despite the frailty of his body.