Yet Mrs Bennet says by the end of chapter 3 that Mr Bingley danced with her... I think it is her younger sisters who are not "out" yet, while maybe older than Kitty and Lydia.
I tend to think to, that Georgiana was "out" at fifteen, when the establishment was created for her.
I tend to think that Jane Bennet was "out" at sixteen, because it is written, sorry I don't remember where in the novel, that her mother had hoped she would marry since her being sixteen (when Mrs Bennet calls at Netherfield whe learn that a young man was in love with Jane when she was fifteen but I am not sure she was out then).
Maybe Elizabeth, being the second, was "out" younger thant Jane.
"chaperoning of young, unmarried women was a privilege of married women"
Of course, hence Mrs Bennet's reflection at the Netherfield ball : "it was so pleasant at her time of life to be able to consign her single daughters to the care of their sister, that she might not be obliged to go into company more than she liked" - which meant that as soon as she would be married, Jane would be able to chaperone her sisters; the narrator telling us just after that it was only words from her, not her feelings, which mean in my opinion that it was the common way of thinking - or of speaking.