The man in this poem is reflecting on the first twenty years of his life, which were focused not on nature, but on himself. Like the high school seniors, this man had little time for much more than the business of living. Now that he has survived two decades he is examining his life. He knows that “Fifty springs are little room” to experience all that he wants.
In the first quatrain Housman accents the simple beauty of nature. The cherry blossoms are ripe and pure; nature at its finest. Life, whether plant or human, seems invincible. But the insertion of, “now” at the end of the first line brings us back to the harsh reality of human mortality. The cherries are, “hung… along the bough” suggesting that the branch will not be able to hold the fruit indefinitely. The life of the cherries is limited, despite their beauty.
The last quatrain is rushed as the poet tries to fit in as much living as he can into the last fifty years of his life. He realizes that there is no possible way he can achieve all of his dreams in the short time that he has left. Unlike high school seniors who spend all their time focused on their next step, this poet knows he has to savor life because it moves to fast to not enjoy it.