There's been a bit of a kerfuffle going on among linguists over the origins and spread of the mysterious ancestral language that spawned descendants as diverse as Latin, German, Anatolian, and Persian. From the western shores of Spain to present day Iran and India, many of the words that people use to make themselves understood have their roots in a tongue that somehow spread across a broad swath of Eurasia not all that long after the end of the last ice age. The question of how that happened--through a diffusion of agriculture and related technologies from the Fertile Crescent or conquest by horse-raising, chariot-riding pastoralists from what is now Northern Turkey--is a complex one. It's also a good reminder that no one, not even in the 'Old World,' has been where they're at today for long in the big scheme of things.
As a teenager I mistakenly thought that Indo-European had to be the first human language, or maybe one of its second-generation descendants. Possibly it was a daughter tongue carried out of Africa to Europe by the very men and women who had first met the neanderthals of the latter continent, and its fracturing lay behind the biblical story of Babel and its tower. Needless to say, there were some significant time scales that I was failing to grasp back then. That, and I had no appreciation of just how mobile our species has been or how fluid its ethnic groups and racial identities are when thousands or even just hundreds of years are flowing by in an eye blink.
Modern humans may have begun to displace Homo neanderthalenis in Europe around 35,000 years ago, but it wasn't Proto-Germans, Celts, Slavs, or Scandinavians who did it. The oldest distinct ethnic groups in Europe, the Sami people of the Scandinavia Peninsula and the Albanians in the modern Balkans, have only been there for about 5,000 years. Previously and since then, humans have swept across Eurasia, interbreeding, being assimilated, and then giving rise distinct populations only to be displaced and mixed up again. The vast grasslands of Western, Central, and Eastern Asia have churned out many iterations of far-ranging horse riders and the tenacious hunter-gatherer tribes who warred with them in the border regions of hills and forests. Members of both groups spread out from those heartlands in distinctive waves of emigration across the rest of the continent.
The entrance into Europe of the Germanic peoples, their conquest of the Celts, and their clashes with the agrarian civilization of the Roman Empire is one such wave that just happened to be documented to a degree by early historians and commentators. And if it was recent enough to find its way to pen and parchment it's pretty much breaking news to species that has been around for the better part of a quarter of a million years.