Better, Faster, Younger: Why baseball's young stars are its best in 20 years

— -- This story appears in ESPN The Magazine's March 28 MLB Preview Issue. Subscribe today!

WISE MEN SAY the first time you feel old is when you look around and realize that most major league baseball stars are younger than you. If that's true, a lot of folks are aging very suddenly. Young studs are everywhere around MLB these days.

Consider the best players in each league and the careers they could have in store. In the NL, that would be 23-year-old Bryce Harper, about whom my colleague Jayson Stark has written: "He's a blend of Pete Rose and Reggie Jackson, as if that were even possible." Actually, it was possible; his name was Frank Robinson. As in the Triple Crown -- winning Frank Robinson who hit 586 career home runs and won the MVP in both leagues. He happens to be the best statistical comparison to Harper in baseball history, according to Baseball-Reference.com. In the AL, it's Mike Trout, 24, and his best comp is Mickey Mantle. As in Mickey Freaking Mantle.

Beyond them, the parade of high-grade youngsters just keeps marching. Jose Altuve, Nolan Arenado, Kris Bryant, Madison Bumgarner and Gerrit Cole were All-Stars last year. Mookie Betts and Carlos Correa will be for years to come. And that only takes us through the first three letters of the alphabet.

To measure just how drastically youth has taken over MLB, The Mag, with the help of Ben Alamar, ESPN's director of sports analytics, studied the past three decades of elite seasons by players -- which we defined as 1 standard deviation or more above average in wins above replacement. Alamar found that, beginning in the early 1990s, the proportion of elite seasons by position players ages 25 and under declined sharply, bottoming out at 5.9 percent in 2002. Then it started to rise, and it has jumped sharply in the past two years, hitting a whopping 34.4 percent in 2015. (The data is similar, though not as dramatic, for pitchers.) In short, young players are producing more great seasons than they have in a generation.

Like hitting and pitching, youth and age tend to move in cycles as sources for MLB star power. Youngsters with Hall of Fame talent don't come around too often, so think about what happens when a few do arrive at about the same time, as Mike Schmidt and George Brett did in the early '70s, or Rickey Henderson, Cal Ripken Jr. and Tony Gwynn did in the early '80s (or Harper and Trout did in the early 2010s). Teams begin to focus on developing their own prospects. If we are lucky, an entire cohort emerges. And as veterans, they dominate the game -- until another crop of rookies is strong enough to replace them, and the seasons change again.

Over time, however, those cycles are trending younger. MLB's relentlessly increasing media revenue keeps driving up the value of wins, spurring organizations to keep improving and innovating the search for young talent. On one front, teams have stepped up their recruiting efforts in Latin America, where spiraling competition has them investing ever more in hotshot teenagers (though signing internationals still costs a fraction of what it would take to sign North Americans with labor rights). In 2012-13, the first summer and winter of baseball's current CBA, the Rays spent $4 million, the most of any club, on international free agents. That leader-of-the-pack figure has since exploded, to $8.4 million by the Rangers in 2013-14, $15.6 million by the Yankees in 2014-15 and more than $44 million by the Dodgers this past year. As analyst Ari Berkowitz noted three years ago: "We've gotten to the point where signing 16-year-old IFAs [international free agents] is no longer a market inefficiency but a competitive requirement."

Domestic scouting, bolstered by sabermetrics, keeps getting better too. A 2009 study by Sky Andrecheck, an analyst who now works for the Indians, found that the expected career WAR of players taken No. 1 in the MLB draft increased by 35 percent from 1970 to 2000, from 19.4 to 26.1, and recent drafts have bolstered the conclusion that early picks are worth more than they used to be. The development and evaluation of young players are also improving. As just one example, more than 70 percent of the prospects who recently ranked in Baseball America's top 100 lists eventually made it into MLB's top 100 players (as ranked by WAR), up from about 60 percent 20 years ago.

As clubs grow more confident that their picks and prospects will actually turn into valuable players, they hesitate less about calling them up at a young age from the minor leagues, as the 2015 season surely demonstrated. And if something goes awry along the way, well, young players also make good reclamation projects. Jose Fernandez was NL rookie of the year in 2013, blew out his elbow, had Tommy John surgery, came back to strike out 79 batters in 64/ innings last year and is now among the Cy Young Award favorites -- and he's only 23 years old.

Meanwhile, the game's showcase talents have shifted. Across MLB, scoring has dipped, keyed by a decline in power, and teams -- again, boosted by analytics -- are quantifying and appreciating defense more. All of which puts a premium on speed, the quintessential skill of youth. If you compare the list of MLB players who generated 5 or more wins above replacement last year to the group of 5-plus WAR players from 2000, three things stand out about the contemporary athletes: As a group, they hit far fewer home runs (24.3 per 600 PA vs. 32.9). They are much better fielders (defense: 19.7 percent of total value, compared with just 4.7 percent). And on average, they're more than a full year younger (ages: 27.7 and 28.8).

Occasionally, external forces have reshaped baseball's balance between youth and veterans. For instance, the average age of players jumped during World War II as athletes were called into military service and teams often replaced them with oldsters who otherwise would have been retired. Pretty clearly, steroids also delivered an exogenous shock to MLB's system. We don't know which players used what chemicals -- or, unfortunately, how much various PEDs actually enhance performance. But average age, power and the percentage of elite seasons by older players started rising in the mid-1990s, when it became common for anabolically supported weight training to extend MLB careers. And they all started declining in the mid-2000s, after the advent of drug testing. We don't need to know precisely what a man drank last night to recognize that he's hungover this morning.

With that era gone, not much is left to hold back the forces pushing baseball to keep getting younger. Smart franchises, like the two that met in last year's World Series, are showing how to stay ahead of the curve: by developing, hoarding and riding young talent.

It's all enough to light up the game for years to come. Even if it makes you feel as old as Honus Wagner.