Posted by Neil Paine on July 14, 2009
...AKA part one of what I'm sure will be a very long series before we've said all we want to on the subject.
Now I'm preparing you guys ahead of time, this is mostly a data/graph dump, and there's a lot of selection bias going on here (then again, I challenge you to find an aging study where there isn't selection bias). But using a sample of all player-seasons since 1978 with >2000 MP, here are the numbers on how a player's age affects his rate of Win Shares per 3000 minutes. The first focus will be every player in the sample, and the average change in their WS3K by age:
If you prefer that in graph form:
So that basically jibes with what we expect to see in an aging curve -- you peak at around age 27, then slowly go downhill until your mid-30s, when you fall off a cliff (unless your name is "John Stockton", apparently: the Pasty Gangsta still had an absurd 11.65 WS3K at age 40!). Still, this is the general curve for every type of player... Can we find differences by position?
Here are centers:
Just like the aggregate player pool, centers apparently peak at 27 (also, keep in mind that the sample size is ludicrously low for Cs). Here are the forwards:
Again, age-27 peak, slow decline until early-to-mid 30s, and then you start to lose it for good. Finally, the guards:
I think the guards are the most interesting, because some peak as early as age 25, some peak at the conventional 27, and some even hang around to peak as late as age 32! Among guards who played more than 1 season of at least 2000 MP, here's the distribution of peak seasons by age:
Here's another interesting tidbit: those who peaked early (before age 26) burned themselves out too soon -- they performed a half a win worse per season from age 30 on than their normal-aging counterparts, averaging 6.84 WS3K after the big 3-0 (as opposed to 7.33 for everyone else).
And finally, there's the question of whether guards tend to lose it quicker, and at an earlier age, than other positions. Here's a table showing what percentage of players in the study were represented at each age checkpoint:
|252 Guards||323 Others|
And let's graph those percentages side by side:
As you can see, on average guards do disappear sooner than players at other positions, starting at age 32. The conventional wisdom is that smaller players who rely on their speed/quickness tend to lose that ability (and therefore their viability as NBA players) in their early 30s; bigger players, of course, lose it at that point too, but it doesn't matter as much for them because they were never very fast to begin with. Based on these results, I'd say the conventional wisdom has been confirmed -- guards do appear to "lose it" sooner than big men, starting in their early thirties. That makes the recent re-signings of aging PGs Jason Kidd and Mike Bibby particularly risky, and the buyer should certainly beware when it comes to Allen Iverson, who could end up being the poster child for this phenomenon.