"An Acre of Grass" is a confessional-style poem, appearing in Yeats' last published collection, Last Poems. I would definitely not classify "An Acre of Grass" as a desired picture of old age; in fact, the poem is quite the opposite and reveals the speaker's dissatisfaction at how his final days have turned out. He is lonely and friendless, with only a mouse for company. "The acre of grass" feels more like a prison, because his aged, weakened body keeps him from exploring the larger world beyond his little plot of grass.
The significance of this poem lies within the speaker's chief sense of regret for how he must spend his "last days." "An Acre of Grass" cleverly illustrates Yeats' malaise; even in old age, the human spirit still longs for more.