There are lots of studies on this sort of thing and they do all suggest age is a factor ??? e.g. this is a fairly coimprehensive study that shows that VO2 max declines past about 35 years of age: <a href="http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.2007.141879/full">http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.2007.141879/full</a> So I think it is right to be suspicious of Horner, but we certainly can???t prove he is doping ??? he may well be a freak of nature ???