Age and Treachery Will Overcome Youth and Skill

It was recently suggested on the AOL STATS Sabermetrics Board that Tony Gwynn's dramatic improvement at age 33-37 is largely due to the fact that the seasons during which he played at those ages coincide with the last expansion in 1993. But I believe there is more to it than this.

While I'm sure expansion has had something to do with Gwynn's improvement, it is an oversimplification to attribute all of it to that one cause. I don't have league numbers for the past 5 years, but I'd venture to guess that Gwynn's BA vs league BA is probably better than just about anyone else's for that same period (heck, only three players--Ty Cobb, Joe Jackson, and Pete Browning--have higher career BAs relative to league averages).

As for the assertion that Gwynn's improvement at such a late stage in his career is unprecedented, let's play a little game of "Who Am I?" I've laid out 5-year stats for two players during the seasons when they were 33-37 years old; I've also given 5-year stats for the same two players during the seasons exactly 10 years prior, i.e., when they were 23-27 years old.

Player A

Age     BA     OBP     SLG     OPS
----------------------------------
33     358     398     497     895
34     394     454     568    1052
35     368     404     484     888
36     353     400     441     841
37     372     409     547     956
----------------------------------
Tot    368     411     508     919

----------------------------------
23     309     355     372     727
24     351     410     444     854
25     317     364     408     772
26     329     381     467     848
27     370     447     511     958
----------------------------------
Tot    338     393     448     841

Player B

Age     BA     OBP     SLG     OPS
----------------------------------
33     285     343     464     807
34     325     399     489     888
35     320     389     461     860
36     332     402     509     911
37     341     410     518     928
----------------------------------
Tot    322     401     488     889

----------------------------------
23     304     372     469     841
24     267     341     335     676
25     302     366     450     816
26     270     333     410     743
27/28  291     344     395     739  
----------------------------------   
Tot    288     348     414     762

Both of our contestants hit significantly better when they were 10 years older. Following are indexes which compare the numbers put up at age 33-37 to those put up at 23-27:

              BA     OBP     SLG     OPS
----------------------------------------
Player A     109     105     113     109
Player B     112     115     118     117

From this it appears that Player B has improved his performance at age 33-37 vs age 23-27 even more than Player A has. There have been numerous factors involved in both players' improvement, including health, experience, and yes to an extent expansion.

Now let's unmask our familiar friends. Player A is of course Tony Gwynn (that 394 BA kind of gave it away); Player B is Paul Molitor. So not only is Tony Gwynn not the only player to improve that dramatically at such an advanced age, he's not even the player who improved the most at that age.

While I am willing to concede that some of the increased success of both Gwynn and Molitor is due to the factors mentioned above, I believe that in both cases they did in fact become much better at an advanced age.