Jeter isn't really helping the Yankees much this year, batting .268 but with just two home runs and the kind of range you'd expect from a 40-year-old shortstop. But he's hardly been the primary problem with the Yankees: Brian McCann, Carlos Beltran and Alfonso Soriano all have a lower WAR.
In honor of Jeter's 40th, I thought it would be fun to look at the all-time age-40 All-Stars, the best seasons at each position since 1901 at that age (via Baseball-Reference.com Wins Above Replacement).
C: Bob Boone, 1988 Angels (3.1 WAR)
Only three age-40 catchers earned at least 1 WAR in a season -- and two of them did it in 1988. Carlton Fisk did it for the White Sox by hitting 19 home runs and slugging .542 in 76 games. Boone, however, edges out Fisk for the highest WAR, as he was still an excellent defender at 40 and started 111 games. Gabby Hartnett, a backup for the 1941 Giants, was third to top 1 WAR.
1B: Darrell Evans, 1987 Tigers (4.9 WAR)
Evans is the easy choice as he hit 34 home runs while drawing 100 walks. No other first baseman tops 2 WAR and only four (Pete Rose, Willie Stargell, Mickey Vernon, Jason Giambi) topped 1. You may think first base is an old guy's position, but not many make it to 40. Only 10 guys even reached 200 plate appearances.
2B: Eddie Collins, 1927 A's (2.3 WAR)
Collins hit .336 with a .448 OBP in a part-time role, good enough to beat out Tony Phillips, Nap Lajoie and Joe Morgan. Craig Biggio and Jeff Kent were still playing second base at this age (Biggio hit 21 home runs), but defensive issues knocked down their WAR.
3B: Graig Nettles, 1985 Padres (3.3 WAR)
Nettles was a terrific glove man earlier in his career and still good enough to play 137 games in 1985. He hit .261/.363/.420 while walking more than he struck out. Chipper Jones' final season with the Braves in 2012 rates second at 2.8 WAR, while Cal Ripken's last season comes in at -0.6.
SS: Luke Appling, 1947 White Sox (4.6 WAR)
Only seven players played at least half their games at shortstop at age 40. Five of them are in the Hall of Fame -- Appling, Honus Wagner, Ozzie Smith, Barry Larkin and Bobby Wallace (who played just 26 games at age 40). The sixth will get there: Jeter. And the seventh is Omar Vizquel, and he may get there as well.
OF: Willie Mays, 1971 Giants (6.3 WAR)
For some reason, at age 40 Mays suddenly decided to start walking a lot more. His previous high had been 82, but in '71, playing just 136 games, he drew 112 and posted a career-best .425 OBP even though he hit .271.
OF: Sam Rice, 1930 Senators (4.7 WAR)
The Hall of Famer was one of the great "old" players ever. He had 426 hits before age 30 but 2,561 after. At age 40, he hit .349 with 207 hits.
OF: Ty Cobb, 1927 A's (4.4 WAR)
How did Cobb end up on the A's? After managing the Tigers to a 79-75 record in 1926, Cobb announced in November that he was stepping down as manager and retiring. A few weeks later, fellow future Hall of Famer Tris Speaker did the same with the Indians. Later, it was revealed commissioner Kenesaw Mountain Landis was investigating Cobb and Speaker for betting and perhaps fixing a game in 1919 (as accused by former pitcher Dutch Leonard). While there was strong evidence bets were made or attempted to be made (Cobb had written in a letter that his attempted bet didn't work out), Landis eventually found the two stars not guilty. When Connie Mack (a man Cobb respected) offered Cobb a job with the A's, he decided to play two more years. At age 40, he hit .357 and drove in 93 runs.
DH: Dave Winfield, 1992 Blue Jays (4.1 WAR)
Winfield hit .290 with 26 home runs and 108 RBIs and finished fifth in the MVP voting.
SP: Randy Johnson, 2004 Diamondbacks (8.5 WAR)
SP: Phil Niekro, 1979 Braves (7.9 WAR)
SP: Cy Young, 1907 Red Sox (7.6 WAR)
SP: Pete Alexander, 1927 Cardinals (6.1 WAR)
SP: Nolan Ryan 1987 Astros (5.4 WAR)
That's a pretty tough group to crack. Obviously, pitchers have a higher rate of success at age 40 than position players. Seventeen pitchers have reached 4.0 WAR or more -- including Bartolo Colon last year -- and 30 have reached 3.0 WAR or more. For position players, the totals are six and 10 (Wagner and Edgar Martinez are the others to reach 3.0).