The kids are here – don't book October yet, St. Louis

JJ Wetherholt led off in his major-league debut, the Cardinals' 2026 home opener at Busch Stadium. In his second trip to the plate, he hit his first big-league home run. By October he was a Gold Glove finalist at second base and a front-runner for NL Rookie of the Year.

Only two Cardinals had homered in a debut that was also the home opener: Eddie Morgan in 1936 and Wally Moon in 1954. Wetherholt made it three.

Wetherholt was one of 13 players who made their major-league debuts for the Cardinals in 2026. That tied eight other seasons for the most since 1924, when 14 did. The latest was 2022.

It was a young lineup. Weighted by plate appearances, the Cardinals' 2026 hitters averaged 25.8 years old on June 30. That was the youngest lineup the franchise has fielded since 1917, when the team averaged 25.7.

History says to enjoy the kids and hold off on playoff plans. Young teams like this one won a little more over the next three years than teams with the same records. They reached the postseason about as often.

The home opener was March 26, against Tampa Bay. In the third inning, Wetherholt hit an estimated 425-foot home run off the Rays' Drew Rasmussen. It was his first hit in the majors, and the sellout crowd called him back out for a curtain call. Later, his sacrifice fly was part of an eight-run sixth inning. The Cardinals came back from 7-1 down to win 9-7.

Two days later, he won a game with a walk-off hit. His two-run single off Griffin Jax in the 10th inning beat the Rays 6-5. Only two other Cardinals had a game-ending hit in one of their first two big-league games: Curt Ford in 1985 and Bill Virdon in 1955. 700 Clark's Deep Scout for March 29 called his first two games an electrifying debut.

Wetherholt came to the plate 619 times in 2026. That was more than the other 12 debuts combined. No Cardinal had more plate appearances in his debut season since Albert Pujols had 676 in 2001.

He hit .242. His 17 home runs were the most by a Cardinal in his debut season since Paul DeJong hit 25 in 2017. He stole 14 bases in 15 tries. MLB Pipeline named him the second baseman on its 2026 All-Rookie first team.

His glove made the strongest case. A stat called outs above average counts the extra outs a fielder makes. An average fielder is zero. Statcast credited him with 25 outs above average in 2026, the most it has recorded for a rookie. Only the Cubs' Pete Crow-Armstrong had more, with 26.

He is also a finalist for the Gold Glove at second base. The other two National League finalists are Milwaukee's Brice Turang and Pittsburgh's Brandon Lowe. He and the Reds' Sal Stewart have led the betting for NL Rookie of the Year. The last Cardinal to win it was Albert Pujols in 2001.

The loudest single game came in August. Joshua Báez saw one pitch in his first at-bat at Wrigley Field on Aug. 15 and hit it an estimated 449 feet. He homered in his next two at-bats, too, the first player ever to homer in each of his first three.

He came up from Triple-A Memphis, where his 34 home runs led Triple-A when he was called up. The next two days were harder. He went 0-for-14 with six strikeouts. He finished 2026 with 7 home runs in 108 plate appearances, a small sample.

Six of the 13 debuts came on Aug. 1 or later.

Bryan Torres debuted at 28 on May 23 in Cincinnati. He homered in the ninth inning of an 8-1 win, the first game of a doubleheader.

Blaze Jordan had two hits in his debut on June 12 in Minnesota. The next day he tripled and homered.

Leo Bernal, a catcher, drove in 2 runs in his debut, a 13-8 win in Los Angeles on Sept. 1. He homered the next day, too.

Quinn Mathews debuted on Aug. 1 in Toronto and allowed 2 runs in 5 innings. He and Luis Gastelum threw the most innings of the 13. Their lines are in the table at the end.

Cooper Hjerpe came out of the bullpen on Sept. 6 in Colorado. He faced 12 batters, got 12 outs and struck out 6.

Of the 30 teams, only the Nationals had a younger lineup in 2026, at 25.3. The 29 teams other than St. Louis, taken together, averaged 28.4.

The pitching staff was young, too. Weighted by innings, Cardinals pitchers averaged 27.9 years old. That ranked fifth-youngest in the majors and was the youngest Cardinals staff since 2018.

Players under 30 hit 163 of the team's 167 home runs, or 97.6%. Pitchers under 30 won 71 of its 77 games, or 92.2%. No other team in 2026 reached 90% in both.

Young means different things in different eras. Across the majors, lineups averaged as young as 27.4 years in 1912 and as old as 30.2 in 1945, the last war year. So we also measured each Cardinals lineup against the rest of the majors in its own season.

Against their own eras, only the 1907 and 1918 teams sat a little further below. The 1938 team was about even. In plain years, no Cardinals lineup since 1917 was younger than this one.

From 1901 through 2022, 95 major-league teams began a run of lineups at least 2 years younger than the rest of the majors. Some stayed that young for years, so we count each run once, at its first season. The 2026 Cardinals were 2.6 years younger.

Over the next three seasons, those teams won about 2 more games per 162 than teams with similar records in the same era, a modest edge. In the very next season, there was no clear edge.

The bars nearly match. The young teams' postseason edge is too small to tell from chance. The lower pairs narrow the field to records like the Cardinals' .475, from .430 to .520. Thirty-one young teams fit, and they did about what the 913 other teams with those records did.

A few examples show the range. The 2014 Chicago Cubs went 73-89. In 2016 they won 103 games and the World Series. The 1933 Detroit Tigers went 75-79, then won 101 and the pennant in 1934. Others went the other way. The 1975 Montreal Expos went 75-87, then lost 107 games in 1976.

These numbers describe what happened to past teams. They are not a forecast for 2027. Young lineups may also have been teams with good prospects on the way, and these numbers do not separate the two.

We did not test whether the young roster explains the 77-85 record. This piece makes no claim about it, and none about why the club built its roster this way.

We did split the history into four eras: before 1946, from 1946 through 1975, from 1976 through 1994, and since 1995. No era stood out. Each era had 17 to 29 young teams, too few to tell the eras apart.

2026 figures come from MLB's official data (statsapi): every box score of the season, summed for each player and team, with birth dates and debut dates. Each team's sums match its season totals. History comes from the Lahman database through 2025, where plate appearances are at-bats plus walks, hit-by-pitches, sacrifice hits and sacrifice flies. Ages are exact ages on June 30 of each season. A lineup's age is its hitters' average age, weighted by plate appearances. Players who made more than half of their appearances as pitchers are left out, so seasons before the designated hitter compare on the same footing with 2026. Players without a full birth date are left out too. A pitching staff's age is weighted by innings. "Under 30" means under 30 on June 30. The two sources agree on birth dates: their 2025 team ages, figured the same way, match within a week. A debut counts for a season when the player made his MLB debut that year and played for the Cardinals. Debut counts cover the National League years, 1892 on. For young teams across the majors, each lineup is compared with the pooled age of every other American and National League team that season. A franchise's young seasons in a row count as one run. The similar-record teams finished within 25 points of winning percentage in the same era. The chart's two lower rows instead set the young teams with records like the Cardinals' beside every other team with those records, from any era. A postseason trip means a division or wild-card title, or a pennant. Debut records come from MLB, and we checked them against Retrosheet's box scores, which cover nearly every debut since 1900. The opener history uses Retrosheet's box scores, which cover every Cardinals opener since 1901. The walk-off history uses Retrosheet's play-by-play of Cardinals home games, which starts in 1908. The 2026 debut games come from MLB's play-by-play. Gold Glove and Rookie of the Year facts come from news reports, listed in the editor's notes.