The Jordan Walker era in St. Louis has begun.

That in itself is a pretty big deal. Walker, baseball’s No. 4 prospect as ranked by MLB Pipeline, reported to Spring Training this season as a 20-year-old non-roster invitee who had never played above Double-A. But when he debuted on Thursday, going 1-for-5 and recording his first career RBI as the Cardinals' starting right fielder in a 10-9 loss to the Blue Jays, he achieved more than just a personal milestone. 

For one thing, it had been a century since a 20-year-old position player had started on Opening Day for the Cardinals. In fact, just four players in franchise history – Frank Snyder (1915), Jack Smith (1916), Rogers Hornsby (1916-17) and Howard Freigau (1923) – had previously cracked Opening Day lineups before their 21st birthdays.

Walker also became the youngest position player to make his Major League debut for St. Louis as part of an Opening Day lineup, edging out Albert Pujols, who was 21 at the time of his debut in 2001.

This also goes well beyond franchise history. In the Modern Era (since 1900), just 108 position players in AL/NL history have started on Opening Day before turning 21. It probably isn’t a coincidence that an unusually large percentage of the players considered fit for the challenge grew up to be better than average – 59 (54.6%) made at least one All-Star Game, and another 20 are enshrined in the Hall of Fame:

• Ivan Rodriguez, Rangers, 1992
• Ken Griffey Jr., Mariners, 1989-90
• Alan Trammell, Tigers, 1978
• Robin Yount, Brewers, 1974-76
• Gary Carter, Expos, 1975
• Orlando Cepeda, Giants, 1958
• Brooks Robinson, Orioles, 1957-58
• Bill Mazeroski, Pirates, 1957
• Frank Robinson, Reds, 1956
• Al Kaline, Tigers, 1954-55
• Henry Aaron, Braves, 1954
• Mickey Mantle, Yankees, 1951-52
• Eddie Mathews, Braves, 1952
• Willie Mays, Giants, 1952
• Ted Williams, Red Sox, 1939
• Bobby Doerr, Red Sox, 1937-38
• Mel Ott, Giants, 1929
• Travis Jackson, Giants, 1924
• Rogers Hornsby, Cardinals, 1916-17
• Ray Schalk, White Sox, 1913

You no doubt remember a few other incredibly young phenoms taking MLB by storm in recent years. Yet it’s become especially rare to see players that young breaking camp as starters – not least because a good chunk of future big leaguers are still playing college ball at 20. Since 1995, just 16 players under 21 years old have been penciled into Opening Day lineups:

• Jordan Walker, Cardinals, 2023
• Juan Soto, Nationals, 2019
• Fernando Tatis Jr., Padres, 2019
• Manny Machado, Orioles, 2013
• Bryce Harper, Nationals, 2013
• Jason Heyward, Braves, 2010
• Elvis Andrus, Rangers, 2009
• Justin Upton, D-backs, 2008
• Miguel Cabrera, Tigers, 2004
• Joe Mauer, Twins, 2004
• Adrian Beltre, Dodgers, 1999
• Mike Caruso, White Sox, 1998
• Andruw Jones, Braves, 1998
• Jose Guillen, Pirates, 1997
• Edgar Renteria, Marlins, 1996
• Alex Rodriguez, Mariners, 1996

A third of the 15 who preceded Walker – Tatis, Heyward, Andrus, Mauer and Caruso – were also making their Major League debuts. Just 41 position players aged 20 or younger have made their MLB debuts as Opening Day starters since 1901. 

What this says about Walker's already very bright future probably isn't much. But the prestige surrounding his debut did make for a fitting end to a spring spent exceeding expectations.