Today Mitchel Lichtman concludes his study on aging patterns. For those of you too "busy" to read the whole thing:
When all is said and done ... we pretty much find that which we already knew -- players peak at around age 27-28, decline gradually until around age 35, and then decline a little more rapidly after that.
We also find that if we split the data up into two eras, pre- and post-1980, there is a slightly higher peak in the latter years (28, as opposed to 27-28 prior to 1980), similar declines until the mid to late 30s, and then a much shallower decline after that in the modern era. That should not be all that surprising given the advances in medical care, better training, higher salaries and perhaps the use of PEDs.
So while I think that we have shed some more light on the subject of peak age and trajectories for the average MLB player (as well as some subsets), I think the issue still contains a lot of muddy water. We don’t really know what the question is or even what it means once we articulate it.
Practically speaking, we are usually interested in the (estimated) peak age and trajectory for individual players and subsets of players in MLB, for projection and salary purposes. To that end, it is probably more useful to frame these questions in a much more specific fashion, such as, "Given that a player has already played five years full-time in the majors, and is a fast and wiry player, and given his trajectory thus far, what is his likely peak age, and what will his future trajectory look like?"
Those are the questions we really need to answer, and we probably shouldn’t concern ourselves so much with the nebulous concept of the "average MLB player’s aging trajectory" -- whatever that even means.
Mickey's exactly right.
Bill James pegged the "peak" 25 or 30 years ago. In the last 10 years, it's become obvious the performance curve has flattened for older players. We can speculate forever on exactly why that has happened, but it's clear that it has.
Those are knowns, and have been for some time. So Mickey's right: the next step is to crack open all that data and see what else we can learn. Do players like Ryan Howard have the same aging curve as players like Chone Figgins? Do pitchers like Mark Buehrle have the same aging curve as pitchers like Josh Beckett?