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. (Chapter 9)

I agree and would add that Kitty and Lydia are undoubtedly less discriminating in partners and may have been soliciting boys their own age who might not be up to asking a lady not one and twenty. This is a public ball; I think it is one where folks can buy a ticket so it is open to anyone—I could be wrong of course. I know Lydia is a little young to be out but I am only speculating boys her own age might be in attendance. Anyway, Line I think you have a good point here. :D