You have to go back a long way to find a common mitochondrial ancestor, because mitochondrial DNA is inherited only through the maternal line. But with genealogical ancestry (which corresponds to nuclear genomic DNA) you have two parents, so your number of ancestors doubles each generation as you look back, and you quickly get overlapping ancestry.
So the most recent genealogical common ancestor of all modern humans was much more recent, probably around 2,300 years ago. And at around 5,000 years ago all modern humans have identical ancestry: everyone then alive was either the ancestor of all moderns humans or of none.
References here:
Could DNA testing verify that someone was a time traveler? - #5 by Riemann
(and subsequent comments in that thread)