Is 600 bce a good date to end the early period of world history? are there any alternatives?

It is good for countries of the western hemisphere because at 600 BCE Classical Greece rose which led to Rome and the West wouldn't exist without these two civilizations. If you are from the far east then it's not that important because the Chinese civilization rose differently. Same could be said for the people in the Americas.

Democracy and darwinism would be my answer.