Yours is a concise but challenging question. Because the genealogies in the Old Testament were not intended to be complete, it is difficult to arrive at accurate dates for some of the oldest events. A common thought is that the Flood of Noah’s day could have taken place some 1,700 years after creation. That is only an approximation by some people.
You might be interested to read “Old Testament Chronology.” It is a short paper from the Wisconsin Lutheran Seminary Essay File.