When the narrator says that Zeena "was already an old woman" at the age of thirty, it does not mean that Zeena physically aged quickly (option A) or that she had many elderly relatives (option C). Instead, it suggests that Zeena had a mature and wise demeanor (option B).
The narrator is describing Zeena's character and personality rather than her physical appearance or family background. By stating that Zeena was "already an old woman," the narrator is highlighting the seriousness, reserve, and somberness that characterized Zeena's behavior. She might have been more reserved, serious, and thoughtful compared to others her age. This mature and wise demeanor gave her the aura of someone older and more experienced.
So, option B, "Zeena had a mature and wise demeanor," is the best interpretation of the narrator's statement. It implies that Zeena displayed characteristics typically associated with older individuals, such as wisdom and maturity, despite her relatively young age of thirty.