As we sit in front of the Hot Stove (or read BCB) and talk about which free agents the Cubs should pursue, we often say something like “Don’t go after Joe Blow.  He’s 34 years old.”  Yet Joe has been consistently productive over the last eight years, still plays good defense, and he bats left-handed.  Will he be productive for us, or will his production suddenly drop off a cliff when we sign him?

I’ve been thinking about this dilemma for a while, and I’ve come up with the concept of “baseball age”, an attempt to reconcile the fact that Andruw Jones seems to be washed up at age 31 and Mark DeRosa seems to still be improving at age 33.  

Baseball age is made up of several components, which I am listing below.  If I were better at math, I would try to quantify this; perhaps someone else already has or would like to try.  I am listing these in what I believe is their order of importance:

1.  Chronological age.  Obviously, this is still the most important component.  As the body ages, it does not recover from stress and injury as quickly, so that muscles and joints don’t function quite as well on a daily basis.

2.  Conditioning level.  This includes cardiovascular conditioning, flexibility training, baseball-related strength training and plyometrics, baseball activity (e.g., throwing), and weight management.  Players who are well conditioned and not overweight place less stress on their joints than players who aren’t and can handle a higher workload more efficiently.  I also believe that players who have maintained their bodies well from the the time they signed their first pro contract age better than those who start at age 30.  Thus, I would expect Jason Marquis to last longer than Ryan Dempster, who had his “come to conditioning Jesus” meeting only last year.  Cliff Floyd lamented last year that he hadn’t taken better care of himself in his younger years; he seems washed up at age 35.

3.  Milage.  I would measure this using innings played for position players, innings pitched for starting pitchers, and appearances for relief pitchers.  Guys who come up at age 21 and play 155 games per season often seem old at age 32.  Guys like DeRo and Plácido Polanco, who start their careers as bench players, still seem strong at age 33.  Career bench players like Alex Cora and Henry Blanco seem to last forever.

4.  Turf.  Vladimir Guerrero is exhibit A.  José Vidro is exhibit B.  I would guess that every inning on turf is worth three on grass.  If you can quantify this accurately, the MLBPA would like a word with you.

5.  Injury History.  Both the number and type of injuries count.  Broken bones, torn ACLs, and torn ulnar collateral ligaments usually heal without incident.  Once a pitcher is completely back from Tommy John surgery, it becomes a non-factor.  How many fans even remember that Chipper Jones had surgery for a torn ACL in 1994?  Other injuries, like a bulging disc in the back, chronic hamstring pulls, or a torn rotator cuff, seriously degrade a player’s performance and shorten his career.

6.  Position.  Catchers take more of a beating than other position players.  Relief pitchers take more of a beating than starting pitchers.  Base stealers take more of a beating than power hitters.  Middle infielders get hit more often than third basemen.  Outfielders’ legs get more wear and tear than first basemen’s.  And Aaron Rowand running into a br...., uh, let’s not go there.

7.  Major Tools.  Speed is usually the first tool to start fading, so players who rely on their speed (e.g., Juan Pierre, Chone Figgins) age very rapidly; players whose major tool is hitting for average and/or power often do very well in their mid to late 30s (e.g., Chipper Jones, Gary Sheffield, Luis Gonzalez, Manny Ramírez).  Players whose main asset is fielding range (e.g., Adam Everett) age faster than players whose main defensive asset is their arm and/or hands (e.g., Chipper Jones, Dwight Evans).  Players whose bat allows them to move down the defensive spectrum will be valuable longer than those whose entire value comes from being high on the defensive spectrum.

8.  Intelligence.  Intelligent players adapt by using their experience to compensate for diminishing physical skills.  An experienced shortstop will compensate for losing a step of raw range by using scouting reports more effectively to help him position himself.  An intelligent pitcher will develop a new pitch to compensate for losing a few mph on his fastball.  Players who don’t adapt (e.g., Marcus Giles) find themselves unwanted at a fairly early age.

9.  Mental Toughness.  As a player ages, it becomes more difficult to push himself to do the extra conditioning work that is needed to compete in a young man’s game, especially as he sees his children growing up.  Jon Lieber seemed to lose the mental toughness needed to keep his weight within reason and his conditioning level high over the last two or three seasons; this manifested itself by his reporting to Spring Training seriously overweight this season and leaving the team in September after he went back on the DL.  He appears to be done.  John Smoltz, on the other hand, seems doubly determined to come back from his shoulder injury and pitch again and he continues to keep himself in excellent physical condition.

10.  Scarcity.  This applies primarily to left-handed relief pitchers.

11.  Luck.  I have no other explanation for Nolan Ryan’s ability to throw 95 mph at age 40.  ‘Nuff said.

Feel free to either come up with a formula to calculate whether Jim Edmonds, Bobby Abreu, or Raúl Ibañez would be more useful to the Cubs in 2009, or flame away at the whole concept.