It is a nice poem. The speaker is 20 years old but is almost lamenting only being able to live in this moment once. He looks back on the moment as if he were seventy yet still looking forward to the future. All time seems to converge in this poem as summer, winter, fall and spring are all mentioned. This implies that what the speaker is doing is capable of defying the laws of nature itself and force all times of his life to exist at once. Now that is just the text itself. Reading into the subtext we can determine what it is the speaker is doing. He is speaking of a cherry tree blossoming which is a common image when describing losing one’s virginity. So it is possible that he is losing his virginity or he is taking someone’s virginity. Knowing that, it makes sense that time seems to disappear. After all, we always remember our first time rather vividly compared to other sexual conquests. A.E. Houseman did an excellent job of expressing that concept.