hi! there's lots to talk about here between Classic Latin and Vulgar Latin, whether you mean native vs simply fluent speakers, and when one considers a language to be no longer "Latin", but fyi, you can get started in the FAQ

• How did Latin "die out"? How did Italian evolve from Latin?

and a few recent posts which may be interesting

• How does a language "die?"

• Was literary Latin ever used in normal conversation?

• Throughout the Medieval and Early Modern periods, scholars who did not share a common language would often write letters to each other in Latin. When scholars visited each other, would they also speak in Latin, or was Latin a purely literary language by this stage?