There is proto-writing, but you are probably more interested in the earliest true representations of language. There are two: Ptahhotep in Egypt and Enheduanna in Sumeria, both around the 25th or 24th century BCE. I know virtually nothing about Ptahhotep, as Egypt is beyond my scope until the Hellenistic period. Enheduanna was a priestess at the ancient city of Ur (in Iraq), and there is a lot of information out there about her and her writing. I think Betty De Shong Meador is still a good place to start for Enheduanna.