We usually let prehistory start with the emergence of mankind. Of course, the planet is much older than that, but that part of the past is studied by palaeolonthologists.
The first human (for what we know nowadays) walked on the earth about 4 million years ago, in East-Africa. Modern man, being the individuals after the Neanderthal people arrived first 35,000 years ago. And first after the last ice age, about 10,000 years ago, the development really started to catch on.
We in the Netherladsn, let prehistory end around the year 0. That is the time, the Romans entered our countries and with that fact we roughly let the historic era start.
In countries further north, like Denmark or Latvia (to mention just a couple) prehistory lasted aboput until the advent if Christianity, around about the year 1.000. And again in America and Australia, one lets prehistory end when these countries are colonised by Europeans, for example from 1492 (Columbus) onward.