The poem is spoken from the point of view of an old man who looks upon the political and romantic obsessions of the young Irish. He suggests that once upon a time he too "talked of love and politics" but that now, with his age and perspective, his thoughts rest on Time and eternal questions. In the final stanza we learn that these meditations are not pleasant, as he suggests that no woman pay him attention due to his age, though he still recalls the women he once loved. The poem ends as he curses Time, which has changed him from young to old.
This poem is based on a conversation that Yeats had with an elderly poet. He wrote in a letter that the peom was "little more than a translation into verse of the very words of an old Wicklow peasant." Wicklow, by the way, is a green, rural county south of Dublin. This precise technique of observation of peasants is what Yeats later recommended to J.M. Synge upon meeting him in Paris, and which led to successful works like The Playboy of the Western World.
The elderly peasant's lamentation is that time has transformed him into someone that is no longer important or viable. This is in contrast to Yeats's other, more wistful and gentle portrayal of age in the rest of the collection. The pikes to which the "old pensioner" refers are the weapons traditionally used in nationalist uprisings against the British, which the man is too old for, so regards as futile.
This poem complicates Yeats' earlier poems, many of which exhort the Irish to contemplate eternal questions like Time rather than take up their pikes, so to speak, for a passing political issue. This old man, who is forced away from politics and love, shows the downside of such contemplative non-participation in life. Of course, he is still tormented by the passions of his youth for women and conversation, and so his meditations aren't exactly what Yeats has in mind in poems like "Who Goes with Fergus?" and "The Man Who Dreamed of Faeryland."