people - approximately 50% of the world's population - speak Indo-European languages.
According to one hypothesis, that is how old the ancestral tongue of the Indo-European languages is. As per this hypothesis, it originated among tribal nomads on the Pontic Steppe, at the intersection of Kazakhstan, Russia and Ukraine. These nomads had significant military prowess and had domesticated horses. Such innovative feats allowed them to spread their language by travel and conquest.
As per a theory put forth by evolutionary biologists from the University of Auckland in 2012, the proto-Indo-European language is even older. As for its geographic origins, they pointed to Anatolia, or modern day Turkey. By their account, the first speakers practiced animal domestication and agriculture. As these practices spread, so did their language.