Disproof mitochondrial eve is 6500 years old

Estimating the age of the so-called "mitochondrial Eve" (i.e. the most recent common ancestor, MRCA, regarding mtDNA) is a very complex issue, exactly for the difficulty in correctly estimating the mutation rate.

So, it is not so easy to disproof the estimate, but at the same time there aren't particular reasons to choose that (and not the several other available estimates) as the correct one.

I point you to three papers that discuss the issues of estimating mtDNA mutation rates and my be of interest for you:

1. Estimation of Past Demographic Parameters From the Distribution of Pairwise Differences When the Mutation Rates Vary Among Sites: Application to Human Mitochondrial DNA
2. Pattern of Nucleotide Substitution and Rate Heterogeneity in the Hypervariable Regions I and II of Human mtDNA
3. Hypervariable Sites in the mtDNA Control Region Are Mutational Hotspots

It will also be an interesting exercise for you to collect from these papers (and the several references therein) all the different estimates of mtDNA mutation rates (and thus of age of the mitochondrial Eve) and you will realize how reliable the 6500 years (without confidence intervals) would be!

Finally, the literature I provide is well established, but also a bit old (but still more recent than the 1997 paper). You might want to see more recent literature.