The Boston Herald continues its series on the state of baseball with a look at the aging of players:

Take a guess how many of today's major leaguers are under 21?

Zero, that's how many.

The 40-year-old baseball player was once a genuine oddity. It's still not as if the majors are teeming with geezers today, it's just that they're getting more attention. Forty-year-old Barry Bonds is the defending National League batting champion. Roger Clemens, at age 42, led the NL in winning percentage last year with an 18-4 record. And then there's that absolute freak of nature, Braves first baseman Julio Franco, who hit .306 last season. Franco celebrated his 46th birthday last August.

Sometimes, however, perceptions don't reflect reality. The Lahman database has enough information to create charts of age for the major leagues. Plotted below are the average age of batters, weighted by plate appearances, and the average age of pitchers, weighted by innings pitched. Click on each graph to get a larger view.

Indeed, the trend in age is up. It's also pretty clear that the money generated by free agency is a big reason. There was a huge dip from around 1950 to 1970 in age. During that time, the owners cemented their grip on the players with the reserve clause and the amateur draft. Unless you were a superstar, there was no reason to stay in baseball into your late 30s. The start of the trend up corresponds to the free agent era. From the article:

There are good and plentiful reasons why today's players hang around, or try to, longer than their counterparts of yesteryear. For one thing, superior conditioning methods (and in some cases, chemical enhancement) mean that they can linger. For another, modern-day salaries offer an irresistable inducement. A few generations back, a 35-year-old future Hall of Famer could make more money selling cars, with less risk of embarrassment, than he might have with another year's baseball salary. Moreover, in today's free-spending baseball world, the only way some teams can sign free agents is by offering long-term, multi-year, guaranteed contracts likely to extend well beyond the useful shelf life of the player.

One thing many have noticed about the numbers generated by the probabilistic model of range is that it was a below average year for baseball in general. Could part of this be having older players taking the field? If not for the anomaly of World War II, 2004 would have had the oldest batters (and position players) in the history of baseball. I have to believe that's hurting defense.

As I think about a number of teams this season, I'm struck by how old they are getting. The Giants, Yankees and Red Sox look especially long in the tooth to me. Last year was the year of the old player. Will this be the year that age catches up to them?

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