Here's a breakdown of why this is significant:
* Age Gap: Roald Dahl was significantly younger than his sister. This gap made her seem like a figure from another world, older and wiser.
* Perception of Wisdom: Children often see older siblings as all-knowing and powerful. The author uses the term "ancient" to emphasize this feeling of awe and respect, tinged with a hint of fear, that he held for his sister.
* Figurative Language: "Ancient" is a metaphor that exaggerates his sister's age and amplifies her perceived authority in his young mind.
* Humorous Undercurrent: There's a touch of humor in the use of "ancient", as it's clearly an exaggeration. It suggests a playful, affectionate, and somewhat ironic view of his sister's role in his life.
By calling her "ancient sister," Dahl evokes a sense of both admiration and distance. It captures the complex relationship between a younger brother and his older sister, highlighting their contrasting perspectives and power dynamics.