I think older guys not keeping up has alot to do with not taking care of themselves. A healthy diet and exercise go a long ways to preserving youth. I'm going on 36 and have a better body, mind, job, etc than a young guy. I can go as long as any female and longer I promise. Age is a bad indicator of stamina, zest and zeal.
However, there will always be preference involved. So if that's your thing then go for it.
As for the study. I think alot of the women that refer to themselves as a "Cougar" pursue younger men in nightclubs and places not associated with good health and longevity. I guess if you go out, don't smoke, limit your alcohol, get your rest, eat healty, and exercise and
F@#$ the study!