How true is that? I see people talking about Sanskrit being 3 to 5 thousand years old. Or was it not a written at that time?
The oldest Sanskrit text, the Rigveda, is usually dated to 1500 BC as an oral tradition. It wasn't written down until much later. The oldest surviving unambiguously Sanskrit writing is from 100 BC, using the Brahmi script. It actually isn't the surviving oldest Indic written language either, the Edicts of Ashoka date to 300 BC and are texts written using various scripts and vernacular languages.