According to the Oxford English Dictionary, singular "they" has a long history going back to 1375. https://public.oed.com/blog/a-brief-history-of-singular-they

According to the Oxford English Dictionary, singular "they" has a long history going back to 1375. https://public.oed.com/blog/a-brief-history-of-singular-they/ https://public.oed.com/blog/a-brief-history-of-singular-they... With a little googling you can verify that Shakespeare, Jane Austen, and Chaucer all used it.