Lydia was a stout, well-grown girl of fifteen, with a fine complexion and good-humoured countenance; a favourite with her mother, whose affection had brought her into public at an early age. She had high animal spirits, and a sort of natural self-consequence, which the attention of the officers, to whom her uncle’s good dinners, and her own easy manners recommended her, had increased into assurance.

– Jane Austen

Pride and Prejudice, Chapter 9. We learn here that Lydia Bennet is a strong 15-year-old who is well developed with "high animal spirits" and is Mrs. Bennet’s favorite daughter. She has "easy manners" and is obsessed with men, especially the officers of her militia regiment. This passage foreshadows the sexual scandal that the flirtatious Lydia will later become involved in.