Once again, I'd like to turn your attention to the fine folks over at The Hardball Times.
Dave Studeman has a long (and worthwhile) breakdown of performance value against contract length. Using his analysis, let's talk about the Yankees bullpen.
In this year's Hardball Times Annual, David Gassko has a great graphic showing that the performance of batters tends to increase until they reach the ages of 27 to 29, then gradually decrease. This is the typical aging pattern known to sabermetricians everywhere. Pitchers, on the other hand, are at their best before the age of 28, after which they gradually decline. And there is no clearly defined peak in the early years--pitchers in their early 20s may have their best years at the age of 22 or 28--the results are rather random.
Obviously, wear and tear on a pitcher's arm is the issue here, but there's also an implication for the distribution of major league pitching talent (and pitching contracts). Since players have to pitch six years in the majors before becoming a free agent, the most production in any given year tends to come from pitchers who aren't yet free agents.
The Yanks are coming to camp with 18 pitchers on their 40 man roster who all want a spot in the bullpen. A 19th, Mariano Rivera, is probably going to be guaranteed a spot. Of those 18, 15 are between the ages of 24 and 28, 'prime' years for a pitcher.
The Yankee bullpen gold standard (Stanton and Nelson) both played with the Yankees after turning 29. They had good years, but they'd both already had their career year by this point (Stanton at 24, Nelson at 28).
The more I learn about what to expect from relievers, the more amazed I am at how lucky the Yankees were to have those two beat the odds at the same time.
I've said it before: let's put that 3 million into next year's draft so that we sign the Mark Priors and Gregory Peaveys of the world.