For those of you folks that read the ARAM rehab post, followed my request to look at this post, I thank you, because I have taken a lot of time to research this, and finally found someone else doing the same research, Bill James.
To summarize the article, Bill James lists a mix of 33 players (obviously, because his article was about the decline of age 33, so it wasn't a coincidence). Names such as Mickey Mantle, Cepeda, McCovey, Brett, Murray, Kaline, Hack Wilson, Duke Snider, Jason Giambi, Ivan Rodriguez, and Albert Belle adorn the list. He shows all of their stats at age 32 compared to age 33, and you notice a significant drop-off.
I've been saying on here for quite sometime now that the prime years of a hitter are about age 26 to 32 years old, and after that, it drops off considerably. Bat speed decreases, injuries mount up, speed on the basepaths diminishes ...