Beneath that cool demeanor beats the heart of a man who played much older than his years in his youth and is trying to turn back the clock in his final season, burning to win as fiercely as he ever did.
"With Derek, it's his competitive drive that makes him the player he is and has been," said former Yankees teammate Raul Ibanez, the current charter member of the 40-something club. "He has the will of a warrior. He's as competitive as any player who's ever played the game.
"I've never bought into judging what a guy looks like on the outside. You never know what's inside him. Derek has a will to succeed in everything he does, and he'll carry that into whatever he does in the future. He's kept it simple and never deviated from who he is and what he does.
"I learned a lot from being around him, his leadership. Great person, great player."
Mariano Rivera, at 43, was the game's oldest player and still one of its best in 2013. The Sandman delivered one of the greatest seasons ever by a player 40 or over, going 6-2 with 44 saves and a 2.11 ERA in 64 appearances.
Having watched Rivera exit so brilliantly without a final postseason fling, Jeter has made it clear he's determined to take his final swings on the October stage, where he carved out his legend for the five-time World Series champions.
If he can appear for a 17th time in the postseason, perhaps he can ease the sting of the fractured ankle that ended his 2012 season in Game 1 of the American League Championship Series against the Tigers.
Before Jeter's injury, that postseason had been the highlight of Ibanez's career. His Game 3 performance in the AL Division Series was among the most remarkable in playoff history.
After his ninth-inning homer against Orioles closer Jim Johnson rescued the Yankees, Ibanez won it in the 12th with another blast off Brian Matusz. In the decisive Game 5, Ibanez singled home a run in a 3-1 victory.
Three innings before Jeter went down at Yankee Stadium in Game 1 of the ALCS, Ibanez unloaded a two-run homer with two outs in the ninth to force extra innings. Jeter's injury in the 12th inning cast a pall over a Yankees loss that led to a Tigers sweep.
Ibanez returned to Seattle in 2013, producing 29 homers and a .793 on-base plus slugging percentage (OPS) for the Mariners. He moved south to join the Angels over the winter, and while he has struggled to find his groove offensively, you wouldn't know it by his behavior.
"I've never heard anything negative come out of his mouth," teammate Mike Trout said.
Trout was six days away from blowing out six candles on his birthday cake in Millville, N.J., when Ibanez made him Major League debut on Aug. 1, 1996, for the Mariners.
Now Ibanez sits to Trout's immediate left in the Angels' clubhouse, making an impression on his superstar teammate as he has so many before him across 19 seasons.
"Raul is such an amazing guy," Trout said. "He'll come in after a tough loss and say, `That's one we've got to win. We'll learn from it.' He's always stressing the positive, doing what you can to get better. And, after all these years, he can still rake."
Ibanez, who turns 42 on Monday, can be found hours before a game at his locker deep in concentration, studying that night's opposing pitcher. His enthusiasm for the game and playing it the right way explain why he's still employed.
"I get so focused on what I'm doing, I don't even know what's going on around me," Ibanez said, looking up from his tablet and apologizing for not acknowledging a reporter.
In superb condition, he has made several game-turning plays in left field and has run the bases with intelligent aggression. But it's his bat, notably in pressure situations, that has defined Ibanez.
He's 15th among active players with 303 home runs and 12th in runs batted in with 1,201.
Cleveland's Jason Giambi, 43, is the only active player older than Ibanez. Rockies closer LaTroy Hawkins, 41, is the National League's oldest player.
Julio Franco, a fit 55, is hoping to chart a new course in his comeback with the independent Fort Worth Cats. Franco was 48 in 2007, playing 15 games for the Braves and 40 for the Mets.
Minnie Minoso, at 54 in 1980, came back to appear in two games for the White Sox.
Legendary pitcher Satchel Paige, at 58 or thereabouts in 1955, and infielder Charley O'Leary, 58 in 1934, are the oldest players to appear in a game - one each - in the Major Leagues.
Paige forged his reputation in the Negro Leagues and on touring teams before coming to the Indians in 1948 at 41 and helping drive them to an AL pennant. Satch being Satch, no one was certain he wasn't closer to 51 than 41.
Durable southpaw Jamie Moyer was 49 in his final season, pitching for the Rockies in 2012. Omar Vizquel was 45 that year, wrapping up a spectacular career.
Knuckleballers wear well. Hoyt Wilhelm was 49 when he stopped floating them, Phil Niekro 48. Charlie Hough retired at 46, Tim Wakefield at 44.
Jim Bouton memorably reinvented himself with the knuckler at 39 after being out of the game for eight years.
Nolan Ryan was in a class of his own in his 40s, winning 71 games and four strikeout crowns after turning 40. The Express struck out 301 batters at age 42 in 1989. In the second to last start of his career, in 1993 in Anaheim, 46-year-old Ryan held the Angels to one unearned run in seven innings, hitting the mid-90s on the guns. Hardball to the end.
Rickey Henderson was another 40-something dynamo. Delighted to be Ryan's 5,000th strikeout victim, the Man of Steal had 25 steals at 42 and a .369 on-base percentage for the Red Sox at 43. At 40, for the Mets, Henderson had a .315/.423/.466 line, stealing 37 bags and scoring 89 runs.
Ibanez attributes his longevity in part to staying open to fresh ideas.
"It's about learning constantly, being open-minded enough to reinvent yourself when you need to change things you've done in the past," Ibanez said. "Not accepting the status quo is part of it. Torii Hunter is a guy I've always admired in that respect. He's constantly evolving as a player."
Another former Angels outfielder who had an influence on Ibanez was Bobby Abreu, who preceded him to Philadelphia, the Bronx and Anaheim.
"I didn't really get a chance to play [regularly] until I was 30," Ibanez said. "For a six- or seven-year span I was definitely a different type hitter, with a different approach and mindset.
"I watched Bobby Abreu a lot. He was always very patient, very relaxed, with a great approach. He was a great hitter, a great player. Tremendous career. It's good to see him still playing."
Abreu, another proud member of the 40-something club, has revived his career this season with the Mets.