I have not yet received a result that might confirm my opinion, but any result I get (after laying out $300 for the test) is now called into question by El Khoury et al. (open source), who show that both the Horvath clock model ,as well as another model by Hannum, systematically underestimate age in tissues from older people. The testing data used in generating this clock did not have a large representation of tissue from elderly individuals, and closer analysis of such date shows a divergence from Horvath's extrapolated line. Details of the analysis are in the open source paper. Here is the summary:
The age prediction properties of both Horvath and Hannum DNA methylation clock models begin to degrade as subjects enter old age. This is at least partly due to saturation, i.e., DNA methylation proportion at some loci approaching 0 or 1, and confounding with the effects of other age-related processes will also play a role. It is likely that this could be ameliorated with additional loci and/or further refined modeling of the currently used set. Association tests using age acceleration should incorporate age as a covariate (as should those using DNA methylation values for individual loci) to avoid spurious associations.
