你年幾歲 Guess How Old I Am
公公道：「你年幾歲了？」行者道：「你猜猜看。」老者道：「有七八歲罷了。」行者笑道：「有一萬個七八歲。公公道：「你年几岁了？」行者道：「你猜猜看。」老者道：「有七八岁罢了。」行者笑道：「有一万个七八岁。
逐句解 Line by line
The old man said, "How old are you, then?"
你年幾歲了 is the question you ask a child, and the old man asks it in earnest. Nothing in the conversation has shaken his reading of what he is looking at.
Pilgrim said, "Have a guess."
Seven characters, and the doubled 猜猜 makes it playful — go on, guess. Pilgrim has spotted that the old man is about to be wrong by a very large margin and is setting the trap himself.
The old man said, "Seven or eight, I should think."
罷了 softens it to a guess offered rather than a verdict — something like, oh, seven or eight, I suppose. The 罷 keeps its full bà, as this project reads it throughout.
Pilgrim laughed. "Ten thousand times seven or eight.
一萬個七八歲 takes the old man's number and multiplies it, which is funnier than naming a real age and also closer to true. 一萬 in Chinese is the standard figure for an uncountable quantity, the way English says a million.
The age exchange is a small set-piece and it is built on one joke: the old man is not wrong about the face. Pilgrim really does look seven or eight. He has been wearing that face for about two hundred characters and everybody has been treating him accordingly.
What makes the reply land is that it is not a correction. Ten thousand times seven or eight is not an age, it is a way of saying you are not even in the right order of magnitude, delivered by somebody enjoying himself.
And it sets up the reveal. Having established that the face is a lie about time as well as about species, the chapter can now afford to take it off.