There are enough people like Hal Higdon, for whom Dr. David Costle measured VO2max to essentially not change from age 36-50, that I have my doubts that age is the primary factor. Other things like consistency, willingness to train hard, injury avoidance and recovery, access to facilities, and staying up-do-date in terms of training theory and physiology are perhaps more important. We have more and more people learning to take better care of their bodies and extend their careers. It's not like 9.93 just came out of nowhere. I just don't think a lot of older athletes work as hard as they did when they were younger.
"Old age and treachery beats youth and skill"