Which team has the youngest lineup in baseball?

You could call the 2018 MLB season "The Year of" a lot of things. The Year of the Dinger, the Year of the Opener, The Year of the Rain Delay … so why not The Year of the Youth Revolution?
The Braves' Ronald Acuña Jr. and Ozzie Albies are just 20 and 21 years old, respectively. Gleyber Torres, manning the infield at Yankee Stadium, born Dec. 13, 1996, has never lived in a world without the internet. Nationals outfielder Juan Soto is 19. He's a teenager who plays baseball like this:

But which team is fielding the youngest starting lineup, overall? To answer that question, we calculated the average age of each team's starting lineup, using their ages as of Sept. 10.
These numbers do not include a team's entire roster. Starting DHs are included for AL teams, and utility players for NL teams. Each lineup also includes a team's ace pitcher.
Surprisingly, the youngest starting lineup in baseball right now does not belong to the Nationals, Braves or Yankees, though the latter two appear in the youngest 10. MLB's youngest starting nine is none other than the Padres.
Without a single starting player over the age of 28, San Diego has far and away the youngest team in baseball. On average, the Padres are just 25.6 years old. Their youth movement is led by 21-year-old second baseman and recent September callup Luis Urias, and his future in baseball could be an exciting one:

It's not all fresh-faced kids, though -- trusty veterans like Eric Hosmer  and Wil Myers  (28 and 27, respectively) share the benefit of their experience without raising the average age too much.
The White Sox, 26.1 years old on average, are chock-full of sluggers in their mid-20s trying to prove they belong on the next competitive South Side team. The Yankees and Marlins both average 26.5 years, but the Yankees have a wider spread in age -- the oldest member of their starting lineup is Brett Gardner, at 35, and the youngest is the aforementioned Torres.
Earlier this year, the Braves fielded the three youngest players in baseball, though that changed after pitcher Mike Soroka went on the DL and Soto debuted in D.C. But they're still a young team, averaging 26.6 years old. And everyone on the team is young at heart, including 34-year-old first-time All-Star Nick Markakis:

The Rays, also 26.6 years old on average, may have two 30-year-olds (Jesus Sucre and Tommy Pham), but they're complemented by Jake Bauers and Willy Adames, who are 22 and 23, respectively.
The Twins, Angels and Royals all hover at or around 27 years on average, thanks to a mix of team icons and young up-and-comers. In the Angels' case, their team icon is keeping their average low -- even though Mike Trout has been in the league for 8 years, he's only 27. (And he's also already historically great but that's another story.)
The Phillies are starting three players over 30 in their lineup (Wilson Ramos, Carlos Santana and Asdrúbal Cabrera), but six players on the roster are 26 or under. Compare that to the Mariners, the oldest starting lineup in baseball, where six players are 30 or over. No player starting for the Mariners is younger than 27.