It’s been 108 years since anyone’s kicked off a baseball season talking about the “defending champion Chicago Cubs,” but it probably won’t be another 108 before it happens again. Not only were the Cubs the best team in baseball last year, winning 103 games on their way to a World Series triumph, they fielded one of the youngest lineups in baseball in doing so.

Average Age of Position Players, 2016

Astros: 26.6
Diamondbacks: 26.7
Phillies: 26.9
Twins: 27
Cubs: 27.4

The Diamondbacks, Phillies and Twins all finished well worse than .500, as did eight of the 10 youngest teams in baseball by this measure. The Astros went 84-78 as the youngest team in the game last season, yet they took big steps to change that this winter, signing 40-year-old Carlos Beltran, 30-year-old Josh Reddick, and 35-year-old Nori Aoki, while trading for 33-year-old Brian McCann. Parents of teenagers don’t age as fast as the Astros did this winter.

The Cubs, however, might actually get younger this year. They let 31-year-old center fielder Dexter Fowler walk away, and will welcome the return of 24-year-old left fielder/catcher Kyle Schwarber from a knee injury. Much of Fowler’s playing time will go directly to Schwarber, and what doesn’t could go to 23-year-old center fielder Albert Almora. The Cubs have veterans in Ben Zobrist (36), Miguel Montero (33). and the newly-signed Jon Jay (32), but on any given day they can start eight players 27 years old and younger. It’s a remarkable thing to say about defending champs.

How remarkable? Last year, the Cubs had the youngest set of position players of any World Series winner since the 1969 Mets, and the second-youngest of any champion in the divisional era.

Youngest Position Players, World Champs, 1969-2016

Mets (1969): 25.9
Cubs (2016): 27.4
Reds (1990): 27.5
Marlins (2003): 27.7
A’s (1972): 27.7
Pirates (1971): 27.7
Giants (2012): 27.8
Twins (1987): 27.8
Cardinals (1982): 27.8
Braves (1995): 27.9

This is a very, very good list to be on. These nine teams, aside from the Cubs, combined for nine pennants and four World Series titles in the five seasons after the listed year. The 1971 Pirates didn’t win another pennant, but they did win three of the next four NL East titles. Only the 1990 Reds — one of the biggest surprise champs of their era — and the 2003 Marlins didn’t have substantial success, and both those teams were saddled with terrible ownership. Winning a championship with a young core is a harbinger of future success.

The 2012 Giants, like the current Cubs, developed their core hitters: Buster Posey, Brandon Belt, Brandon Crawford and Pablo Sandoval. That group would win a second Series, the team’s third in five years, in 2014. The ’82 Cardinals would get back to the Series in 1985 and 1987 with Ozzie Smith, Tommie Herr, Willie McGee making contributions to all three. The ’72 A’s went on to win the next two AL pennants with young stars Reggie Jackson, Gene Tenace, and Joe Rudi.

The flip side of these coins see comparable numbers in the aggregate … but with one catch.

Oldest Position Players, World Champs, 1969-2016

Diamondbacks (2001): 31.9
Yankees (2000): 31.3
Yankees (1999): 30.9
Red Sox (2004): 30.6
Royals (1985): 30.7
Phillies (1980): 30.6
Yankees (2009): 30.4
Yankees (1998): 30.4
Red Sox (2007): 30.2
Phillies (2008): 30.1
Yankees (1996): 30.0

Run the same calculations we did for the young teams, and you find that this group did very well for itself: 15 pennants and eight World Series over the next five years. However, there’s a lot of double-counting, because the 1996, 1998, 1999 and 2000 Yankees teams eat up more than a third of the sample. Those teams had Derek Jeter, Bernie Williams and, beginning in 1997, Jorge Posada. Their average age belied their status as a dynasty built around a young, homegrown core.

There are any number of ways to build a championship team. One championship team, anyway. Sustaining success, though, means bringing a clutch of young hitters together at once and letting them develop together. The Cubs have the youngest lineup core of any champion in nearly 50 years, and the track record of teams that win with a young core is exceptional. Look for the Cubs to be an October fixture for years to come.

Joe Sheehan is a founding member of Baseball Prospectus and a contributor to Sports Illustrated. You can follow him on Twitter here.