Age
We know that Maria Lucas is younger than Charlotte and that Kitty goes out of her way to call on her towards the end of the novel. This suggests that Maria is around 18, though this is not for certain.
Family and Situation
Maria is the daughter of Sir William and Lady Lucas, making her also the sister of Charlotte and the other Lucas children. While we know that the Lucases are tradesman-turned-gentry, we don't know when the switch happened, so we have no information about whether Maria would remember a time before the family relocated to Lucas Lodge.
Character
We not spend much time as readers in Maria Lucas’s presence and few of the protagonists pay her any mind, even when she is in the scene. The narrator, speaking a bit from Lizzy’s point-of-view describes Maria as “a good-humoured girl, but as empty-headed as” her father. Overall it’s likely that Maria is young and silly and does not meaningfully contribute to conversation.
It is entirely possible that Maria is newly out in society. We know she must be “out” by the time the novel begins because she dances with Mr. Bingley at the Meryton Assembly, but at Rosings, we’re told she is uneasy because she “had been little used to company.”
