3000 BC, Indo-European.
So before the split between the Satem and Centum languages? Speakers of PIE?
Probably varies, the natural climate cycle in Central Asia caused the various pulses out followed by gradual population recovery as the climate warmed. Whoever was left around there at the end of the prior mass emigration tended to be the basis for the languages spoken by the eventual next emigration.
https://en.wikipedia.org/wiki/Centum_and_satem_languages
https://web.archive.org/web/20090818002723/http://www.comp-archaeology.org/18LINGUI.htm#
https://omniglot.com/writing/pie.htm