Starlin Castro.

That list, if you can't or don't want to click through, has four players besides Castro on it: Alex Rodriguez, Arky Vaughan, Rogers Hornsby and a guy named Dick Bartell, who looks to have been the Edgar Renteria of his day. That's a very good list! But you and I know it can be easy to make impressive lists with narrow parameters. So let's make it simpler. Let's just make it incredibly simple: What's the list of shortstops with 1,500 plate appearances through age-22 season? (Castro has 1,542; he should get closer to 1,800 or 1,900 by the end of the season, but we're keeping it simple, and we would rather have him near the middle of our parameters than at the bottom.)
That list: Robin Yount; Renteria; Rodriguez; Elvis Andrus; Vaughan; Travis Jackson; Alan Trammell; Hornsby; and Garry Templeton. Nine players, five Hall of Famers (if you'll indulge me and count Rodriguez), plus an active Andrus. And that's why I wrote the (perhaps sensational) headline that I wrote.
But maybe that's still a manipulative list. Let's get even simpler, and simply limit it to ALL position players with 1,500 plate appearances through age-22 season. Now we have 59 players, 52 of whom are retired, 23 of whom are either in the Hall of Fame or are Ken Griffey, Jr. Knowing nothing about Starlin Castro except his age and how much he has played, we can say he is in a group from which 44 percent of players have become Hall of Famers. Which would still justify a similar, if slightly less confident, headline.