I feel like similar things could be said of many places in the world, but surely you wouldn't consider, say, the country of India to stretch as far back? Or Italy? Turkey?

Even sticking with China, surely the mongol led Yuan dynasty is worth separating from before and after it, if you're considering modern borders. Like, does Mongolia get the same claim as China does in that case for oldest country? It kinda becomes a fuzzy question to me. There's got to be a better academically defined way.