At the beginning of Chapter 5 we are told a little about the Lucases. Sir William and Lady Lucas "had several children. The eldest of them, a sensible, intelligent young woman, about twenty-seven, was Elizabeth's intimate friend." This is Charlotte, of course. There is obviously at least one other Lucas daughter, since we also read, "That the Miss Lucases and the Miss Bennets should meet to talk over a ball was absolutely necessary ... ." [emphasis mine]

Now, if a 27-year old Lucas daughter was an intimate friend of a younger-than-23-year old Bennet daughter, does that mean that the other daughters were younger than Elizabeth? Or perhaps they were just not as sensible and intelligent as Charlotte?

We don't learn much about the Lucas siblings other than Charlotte in this chapter, except that there is at least one young Lucas son who was visiting the Bennets with his sisters. And he gets into a silly argument with Mrs Bennet, in which Mrs Bennet manages to act as immaturely as the young Lucas lad. :-)