Thank you so much everyone. I clearly understood. In this case, there is no big difference, but I feel using the word "entire" is a bit more intensive. :)

Since Charlie Bucket is a person, so it is assumed that he is the luckiest person. This is okay in speech. "Whole" comes from "unhurt", and means a single object that has not been subdivided. "Entire" comes from "complete", and means no part has been left out. They are different when you are talking about collections of objects; the entire lot of cars, or the entire staff, since these are collections of distinct objects. You would say a whole loaf of bread or a whole person, since these are single objects not usually considered a collection of parts. The expression "whole life" considers one's life to be a single unit that has not been subdivided. An "entire life" means all the parts (years? experiences?) of a life. In this case either could be used.

Benben is right, in this case, there's absolutely no difference. Btw, it looks like you've missed a word in that sentence. "Charlie Bucket was the luckiest ???? in the entire world."

I guess, in this case, no big difference between them.