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08/04/10 1:29 PM ET

Will A-Rod be the last Club 600 member?

At current rate, exclusive list may lock out future entrants

Club 600 used to be one of the most cliquish clubs in town, that little hideaway down a dark alley with no sign above the entrance and a burly bouncer blocking the door. The proprietor was a guy by the name of George Herman Ruth. He built the place in 1931.

Membership at this club was limited. Extremely limited. Over the course of 40 years, only two other guys got in.

Alex Rodriguez/600

Over time, however, the secret got out, the membership expanded. In fact, in the past decade, it doubled. And on Wednesday, when Alex Rodriguez connected on No. 600 against the Blue Jays' Shaun Marcum, it swelled to seven.

A-Rod's career home run total ascended to 600 so quickly that it's easy to take the tally for granted. But the truth is, in the wake of an era obviously impacted by performance-enhancing drugs, Club 600 might again attain the level of exclusivity it once possessed.

After Ruth founded the club on his way to No. 714, Willie Mays joined in 1969 and wound up finishing with 660. Hank Aaron followed in 1971, en route to 755.

For a long while, it was quiet. Then the door swung open and the horde came in. Barry Bonds in 2002. Sammy Sosa in '07. Ken Griffey Jr. in '08. And now, A-Rod.

Four guys in eight years. Not a normal pace.

But don't get used to this rate of progression. Only two active players, Jim Thome (577) and Manny Ramirez (554) are knocking on the 600 Club's door. And only one guy 30 or younger, Albert Pujols (392), is at least nearing the zip code.

Magnificent mashers
Fewest at-bats to reach 600 career homers
Rank Player At-bats
1. Babe Ruth 6,921
2. Barry Bonds 8,211
3. Sammy Sosa 8,637
4. Alex Rodriguez 8,688
5. Ken Griffey Jr. 9,042
6. Willie Mays 9,514
7. Hank Aaron 10,014

"Thome is close," said David Vincent, a member of the Society for American Baseball Research and a noted home run historian, "but how much longer is he going to play? Manny seems to be slowing down. Down the active last after that is Chipper Jones, Vladimir Guerrero, Jason Giambi, Andruw Jones, Jim Edmonds, Albert Pujols. You have to get to Pujols to say, 'Here's somebody who maybe could get there.'"

Thome knows he'll only get there if his body cooperates and he keeps finding a taker for his DH-only services.

"You think about it," Thome admitted. "It's close ... If you play the game, and all that stuff works out, it would be wonderful to accomplish it."

But what about the names further down the list? How about Prince Fielder (184) or Ryan Howard (245)? Surely, they've displayed a penchant for power at this still-early stage of their career, but will it last?

"It's about bulk of years, how young you are when you make it to the league," said Fielder's teammate, Ryan Braun. "Prince hit 50 at age 23, and that's as impressive as anything. The younger you are when you make it to the league, the better chance you have, but it's still so hard to predict power, predict development and whether a player is going to be able to avoid injury."

With the game cracking down on performance-enhancing drugs, we're beginning to see more realistic numbers, more susceptibility to the injury bug and Father Time.

Still, that doesn't sway some from thinking Club 600 will continue to welcome its share of new members.

Who's after A-Rod?
Active homer leaders after Alex Rodriguez
Rank Player Age Homers
1. Jim Thome 39 577
2. Manny Ramirez 38 554
3. Chipper Jones 38 434
4. Vladimir Guerrero 35 428
5. Jason Giambi 39 412
6. Andruw Jones 33 403
7. Albert Pujols 30 392
8. Jim Edmonds 40 390
9. Paul Konerko 34 352
10. Adam Dunn 30 342
11. David Ortiz 34 339
12. Todd Helton 36 327
13. Lance Berkman 34 326
14. Carlos Lee 34 321
15. Troy Glaus 34 318

"I think the training people are getting today and the sports-specific training they're going to be getting more and more of in the future is going to allow swings and players to get better," said Bobby Valentine, former Rangers and Mets manager and current ESPN analyst. "I think in the future, there's going to be plenty of guys reaching that milestone. Whether it's a Jason Heyward at 20 years old or a Mike Stanton at 20 years old right now, if we're looking at 20 years from now, I think the 600 mark is very reachable for them and many other athletes that are going to come along."

Vincent is not as sure.

"Until a guy hits a few hundred homers, where there's more numbers behind it, I wouldn't trust it," Vincent said. "I've been fooled so many times by guys that you think may have got it locked in. But then something happens to throw it off. People are talking about this kid in Atlanta, Heyward. Already, he's gotten hurt. So who knows?"

More than 17,000 men have played Major League Baseball, and fewer than 800 have hit 100 home runs in their career. So when a young player reaches 100 quickly, it is easy to forecast that he might one day reach the kind of level A-Rod has ascended to. But the game's rate of attrition speaks for itself.

Guerrero, as an example, was 30 when he reached the halfway point in 2005. He's 35 now and has hit 128 in the time between. Thome hit No. 300 when he was 31 years old. He'll turn 40 in August, so the clock is ticking.

Those who manage to keep up the pace are the rare breeds, and A-Rod is rarer than any of them. He joined the club faster than anybody in history, and by a long shot. He turned 35 on July 27. Ruth, previously the quickest to 600, was 36 years, 196 days old when he hit No. 600. Aaron was a couple months past his 37th birthday. Mays, Bonds, Sosa and Griffey were all 38.

Rodriguez's path, then, was a circumvented one, and it could be a long, long time before anyone comes within striking distance of 600 so quickly.

If Thome's body holds up, maybe he'll join the club. Ramirez might do it, too. But after that, the wait between entries could be a bit more in line with the historical flow, rather than the recent flood. Club 600 could become the little hideaway that it once was.

Anthony Castrovince is a reporter for MLB.com. He blogs about baseball at CastroTurf. This story was not subject to the approval of Major League Baseball or its clubs.