This is a famous poem called "Father William", written by Lewis Carroll. It is a conversation between a young man and an old man, Father William, who seems to be full of life and energy despite his advanced age. The young man questions Father William's actions and abilities, and Father William responds with humorous and witty answers.
In the first stanza, the young man comments on Father William's old age and asks him why he constantly stands on his head. Father William responds by saying that he used to worry that standing on his head would harm his brain, but now that he's sure he doesn't have a brain, he does it anyway.
In the second stanza, the young man comments on Father William's weight and asks him how he managed to do a back-somersault at the door. Father William responds by saying that he used to keep his limbs supple with an ointment he would sell for a shilling box.
In the third stanza, the young man comments on Father William's weak jaws and asks him how he managed to finish the goose with the bones and the beak. Father William responds by saying that when he was young, he argued each case with his wife, and it gave him the muscular strength that has lasted his whole life.
In the fourth stanza, the young man comments on Father William's steady eye and asks him how he managed to balance an eel on the end of his nose. Father William responds by saying that he's already answered three questions, and that's enough. He tells the young man not to give himself airs and to be off, or he'll kick him down the stairs.
Overall, "Father William" is a humorous and playful poem that uses witty responses to highlight the wisdom and vitality of age.