I got this info from Family Tree a few days ago in response to a similar questions as yours; Hope this will be of some help.

"Mutations do not occur very often; in fact, if two people have the exact same mutations (with none left over) as one another in both the HVR1 and HVR2 regions, then they share a common ancestor sometime in the last 30 generations, or about 750 years. With each mutational difference, we must push back that estimate a very long way".

HLee