What is Yeats's poem, "An Acre of Grass" about?

"An Acre of Grass" is from Yeats' "Last Poems" (1939). The poem graphically describes the plight of the old and aged W.B.Yeats. He realises that he has come to the end of his life and reveals to us the loneliness and joylessness of his sad situation "at life's end."

He first bemoans his weakened and restricted physical state. He is confined to "an acre of grass" which serves as an exercise ground. He has only a few books and pictures to look at. He has no human companions. His only companion is the mouse which keeps him company during his insomnia.

But worse, Yeats feels saddened  that the intellectual frenzy and fire has been completely extinguished and pleads that somehow he become like King Lear, Timon of Athens, William Blake or Michael Angelo who even in their old age asserted their individuality and were creative and productive:

"Grant me an old man’s frenzy,
Myself must I remake
Till I am Timon and Lear
Or that William Blake
Who beat upon the wall
Till Truth obeyed his call."

The single common characteristic of all these great men was their misanthropy. In their old age all of them realised their foolishness in trusting their friends or family members who abandoned them in their old age.