In reality nobody has a clue.
The earliest remains found to date put the rise of modern man at around 200 to 300 thousand years ago. They no doubt had some form of a language given that they had the capacity to think and make sounds.
We also know that Neanderthal lived at the same time as modern man, they even interbred and today roughly 4% of our DNA originated from them, they probably had some form of language as well.
Modern man was predated by 19 earlier "versions" of man. Some of those probably had some form of a language as well. (Kinda blows the whole Adam and Eve idea out of the water as to being the first people.) Now you are back over 4 million years.
When people today ask what was the earliest language they tend to forget all of this. But you have to start by defining what you want to accept as a language. These ancients didn't keep written languages but neither do many of today's more primitive cultures, that doesn't mean that they don't have languages.
There is little if any doubt that by 150,000 years ago people had complex and varied languages and even that is being rather arrogant in saying that languages didn't exist before that time line.
In all probability they weren't all that different from languages spoken today. The ancients left very little in the way of evidence, humans don't tend to be very good candidates for fossils but we find the occasional bits and pieces and we find tools and other things they used. Sadly they didn't invent the tape recorder so we will never know what it sounded like to live among them.
But there is no logical reason to think that they didn't have complex and regionally varied languages just as we do today.