Yanks' 'Core 4' aging ... but this fast?

My friend Allen Barra on some surprising projections for a quartet of aging Bombers:

If Nate Silver is correct, both the Democratic Party and the New York Yankees might be headed for tough times this fall. The ace political pollster/baseball analyst projects the numbers for 1,600 major league ballplayers in the current Baseball Prospectus 2010, and things don't look good for the Yankees' "Core Four." Derek Jeter, Jorge Posada, Andy Pettitte, and Mariano Rivera average out at 38 years of age, and no team in the major leagues is anywhere near as dependent on four aging players as the Yankees are.

Based on the study of hundreds of players in their declining years, Silver projects these slides for the Yanks' elders in 2010:

Jeter from a 2009 batting average of .334 to .286 this year, a drop in home runs from 18 to 11, and in stolen bases from 30 to 10. Posada from a .285 BA to .263, home runs from 22 to 12. Pettitte from 14-8 and an ERA of 4.06 to 10-11 and 4.70. Scariest of all, Rivera from 44 saves to 22, and an ERA that moves from 1.76 to 3.53.

Actually, Nate Silver's not running Baseball Prospectus' PECOTA projections anymore; he's too busy with other things. I'm sure PECOTA's new masters are plenty bright, but I simply don't believe these particular numbers.

It's not easy for me to write that sentence, because 1) I like the people at Baseball Prospectus, and 2) for a long time I've been railing against "analysts" who rail against a system simply because they don't like the output.

But I'm not railing against the system. I don't know enough about the guts of PECOTA to rail against it. Instead I'll just say that I don't believe that Jeter is going to steal 10 bases this season, and that I don't believe Mariano Rivera will save only 22 games. I will say, too, that if your system says those things, it's probably worth checking under the hood just in case one of the belts is running a little loose.