Let’s say a modern-day Chinese person who speaks standard Mandarin went back in time while staying in the geographic location of China. How far back would they be able to go while still recognizing the languages spoken as Mandarin or at least some sort of dialect? I understand that the question may perhaps be absurd but I’m still curious. Chinese experts are preferred but anyone may answer. If further details are needed, just ask.

Edit: As a bonus, would anyone have any info on what old and Middle Chinese sounded like?