Miss Brill is probably a woman who is slightly past middle age because she seems rather old-fashioned, wearing a necklet that she has owned for some time. She also ranks other people that she sees as either "young" or "old."
In the story that is told from the perspective of Miss Brill, the reader notes when Miss Brill goes to the park to listen to the Sunday concert that she observes: "The young ones, the laughing ones who were moving together, they would begin...."
Later, Miss Brill alludes to the very "old invalid gentleman" to whom she reads the newspaper four times a week. This activity suggests that Miss Brill is older because usually young people do not want to read to really old people, nor do they have the time. Also, her association with this man suggests her connection to an era that is now obsolete. Further, when the old gentleman asks if she is an actress because of the way that she reads, Miss Brill smooths the newspaper as if it were a manuscript of a play and says with kindness, "Yes, I have been an actress for a long time." This remark may have the hidden meaning that for years she has pretended to be someone she is not because she has not married or has no children. She may even have called herself an actress because she has accomplished little that is significant in life.
After a while, as Miss Brill listens to the music and hears something "so beautiful--so moving..." her eyes fill with tears in her sentimentality, an emotion usually more reflective of a woman who is, at least, middle-aged. Also, she thinks to herself:
Yes, we understand, we understand, she thought--though what they understood she didn't know.
Then, when the "boy and girl" sit down where the "old couple" had been, the middle-aged Miss Brill notices that they are infatuated with each other. In her romantic mind, she thinks, "They were beautifully dressed; they were in love. The hero and heroine, of course...." as she sings along, soundlessly to the music being played.
Miss Brill then hears the girl tell her boyfriend, "No, not now....Not here, I can't." The boy asks her why not. "Because of that stupid old thing at the end there?" the boy asks. "Why doesn't she keep her silly old mug at home!" And, the two laugh at the little fur of which she has always been so proud.
Hurt by the young couple's remarks and giggles, Miss Brill returns to her "room like a cupboard" without stopping as she usually does for a "tiny present" for herself at the bakery. Once in her room, she sits for some time without moving. Finally, she puts away her obsolete little fur in the little box and she thinks that "she heard something crying." Such sentimentality is usually indicative of an older person who was young in another era.