Sky Kalkman and myself had an interesting debate on peak years. He said it was 25-29, while I insisted it was 27-31. He pointed me in the direction of Tom Tango's peak study, which examined players from 1919 to 1998. However, my own study ranged from 1973 to 2008, as I was more interested in what modern players experience as their peak. Is there a discrepancy because of the era that was studied?

What Sky contended was that 31-year-olds have a lot more opportunities to play than 25-year-olds (skewing the numbers in the favor of the 31-year-olds), because the older guys are 'proven' and perhaps have higher salaries and less minor league options that make it tougher to get rid of them.

I suggested that perhaps the difference in conclusions was due to advances in medical/physical training that allow modern players to perform at a high level into their early 30s. When you include players from before the modern era (which I tentatively define as beginning in 1973, e.g. free agency, the DH, divisional playoffs, PEDs, etc.), it changes the results. I can believe that through the whole history of baseball, prime is 25-29, but like I mentioned, I'm more interested in the prime of modern players.

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Fewer people attended college before 1973, so it would make sense that professional careers began earlier then, so their peaks would begin earlier too. Now, baseball peak is not necessarily physical peak - it's where a player's declining talent meets up with his improving experience. As we've seen from the Olympics (and our personal experiences), most people's purely physical peak is around 21. It's quite possible that the average MLB player's peak was 25-29 from 1919 to 1998, because despite the fact that their talent was declining, their experience was increasing. (And I wouldn't doubt that a 25-year-old is more physically talented/in shape than a 31-year-old.) Now that players begin their careers later, doesn't it make sense that the experience part of their peak would correspondingly come later as well?

Not to mention all the medical/physical training advances (life expectancy has gone up more than 20 years since 1919) made that allow players' bodies to remain in top shape longer. So if the drop in their physical shape is not as drastic as it used to be (from the late 20s to the early 30s), while their experience goes up just as much as always, why wouldn't peak also last a few years longer?

What I intend to determine is the rookie age for three periods of baseball history: 1919-1941, 1946-1972 (WWII skews everything), and 1973-present. It's also possible (or even probable) that because of the major changes in the economic situation of MLB since 1973, teams keep players in the minors longer so as to not 'start their clock' until an age when the team would get the most value before the player hits arbitration (and then free agency). So this study of rookie ages should help determine that.

What I believe it will show is that peak WAS 25-29 (from 1919 to 1998) because players overall were younger.

Looking at rookie teens in MLB should tell us the trend for each era. 1919-1941 (with an average of 16 teams per season) had 97 rookie teenagers, 1946-72 (with an average of ~20 teams) had 241. But the current era, 1973-2008 (with an average of ~27 teams), has had the fewest by far: 54 (Justin Upton being the most recent in 2007). Without even calculating for percentage, it's safe to say that modern careers start later.

(I also calculated rookie ages up to 21 and found the same pattern: the earlier you go, the more youths you see.)

But are players going into their 40s as often?

1918-1941: 58 players were at least 40

1946-1972: 62

1973-2008: 163

Percentage-wise, it's rather similar between all three eras (because the modern era has the most teams/players). So players seem to be playing about as long. I expected to see far fewer 40+s in the older eras. To speculate, perhaps players are retiring at the same rate now despite being healthier because they have the financial freedom to. Did a lot of players force themselves to play for the paycheck in days past? Regardless, the rookie ages clearly show that the farther back you go, the earlier careers began.

To sum up, I believe peak is now later because:

- Players begin later (due to higher college attendance and teams not wanting to 'start the clock' until later because of money/value), meaning the experience aspect of their peak correspondingly occurs later than it used.

- They have better physical training/medical knowledge that allow them to stay in shape and come back from injuries faster (or at all), meaning their physical prime is extended.

- Players aren't overused (especially pitchers) due to the aforementioned money that's invested in them and the superior usage knowledge we now possess.

Some other studies support this:

hitters, by JC Bradbury

pitchers, also by Bradbury (plus I like that he uses 1980-2003 as his sample)

Cyril Morong