Mariano Rivera turns 42 today.

It's just a number.

Actually, it's his number. He's the last major leaguer to wear 42, which I think is a shame. Which would honor Jackie Robinson's number with greater effect? Consigning it to outfield walls? Or allowing great and dignified figures like Mariano Rivera to perform brilliantly on the field, as Robinson did?

Well, you know what I think. And it's all water over the dam. Rivera's going to be the last 42, and that's that.

According to Baseball-Reference.com, there have been only 25 relief pitchers in major-league history who pitched at least 20 innings in their Age 42 seasons.

Two of them -- two of the very best of them -- were knuckleballers: Hoyt Wilhelm and Dutch Leonard. Two of them pitched during World War II, when anyone with a pulse and a draft exemption was allowed to pitch. One of them was Satchel Paige.

What they haven't been is closers.

With just one exception: Dennis Eckersley.

In 1997, Eckersley's second season with the Cardinals -- but his 11th with Tony La Russa -- he racked up 36 saves. It wasn't a real good season otherwise, though. He blew seven saves, lost five games, and posted a 3.91 ERA.

Eckersley's the only 42-year-old modern closer. For a whole season, anyway. Trevor Hoffman was 42 in 2010 when he lost his job in May.

Mariano Rivera probably isn't going to lose his job in May.

See, Mariano Rivera has shown exactly zero sign of showing his age.

At 41, his walk rate was lower than his career walk rate.

At 41, his strikeout rate was higher than his career strikeout rate.

At 41, his strikeout-to-walk ratio was significantly higher than his career strikeout-to-walk ratio.

And while he doesn't throw quite as hard as he once did, the difference is small enough to be irrelevant.

There has been just one nod to Rivera's technical, numerical age: He's not throwing quite as often as he used to. When Joe Torre managed Rivera in his late 30s, he would throw 70-80 innings per season. Under Joe Girardi's yoke, Rivera's been throwing only 60 innings per season. He's throwing fewer innings in slightly fewer games.

Would Rivera have pitched just as well in 2011 if Torre were still running him out there 65 times per season, 70-some innings? We'll never know. I sort of think he would have. But it's hard to argue with the results.

We've never seen anyone like Mariano Rivera before. Because he's never been anything except brilliant, it's difficult to imagine him being anything less than brilliant.

It will happen someday. It's just impossible to say when.