When I teach this one of the challenges my students have is to think through the allegorical nature of this tale and consider what qualities or vices the four main characters who drink the potion of eternal youth represent. To work this out, you need to make inferences based on how they are described, what they do and what they say. An inference is a kind of a guess when we do not have the full information but only have clues that we need to think about and consider to come to a conclusion.
Therefore, considering the Widow Wycherly, for example, note what she says in response to Dr. Heidegger's presentation of the potion:
"Nonsense!" said the Widow Wycherly, with a peevish toss of her head. "You might as well ask whether an old woman's wrinkled face could ever bloom again."
Note also what the narrator has told us about Widow Wycherly and how she was a "great beauty" in her past. Think too of how she reacts when she regains her youth and likes the attention she receives. It is clear that we can infer from these clues that she represents vanity in the story. Think now of the other characters and what they might represent. Good luck!