It’s hard to believe, but Carlos Pena turns 30 pretty soon.

Once, Pena was an early-20-something, potential stud first baseman with a sculpted body made for power hitting. And a nifty glove to match. He had the physical good looks and the baseball tools to be one of the best, most charismatic players of his brethren.

Then Pena lost his way, and nearly disappeared from Major League Baseball. In a flash, he was a late-20-something, pedestrian first baseman who would never realize the greatness once seemingly reserved for him.

In 2007, Pena — the former Tiger who was supposed to be the team’s first sacker for years — showed up to spring training with the Tampa Bay (Devil) Rays, without a big league contract and without a promise. He’d have to earn his way — just like any other non-roster invitee, which he was, for one of the worst teams in MLB. He was coming off a 2006 in which he had all of 33 at-bats with the Boston Red Sox. He teetered on the brink of being known as an ex-big leaguer who was long on promise but short on results.

I remember Pena’s first game in a Tigers uniform. He had just been acquired from the Oakland A’s in a complicated, three-team deal that included the New York Yankees and that sent Jeff Weaver to the Bronx. Another player would be coming from Oakland in the trade, as the famous “player to be named later.” The player’s inclusion was designed to simply even up the body count. The player was a righthanded pitching prospect named Jeremy Bonderman. Anyhow, the Tigers were in Boston on that summer day in 2002. And here came Pena, with the smooth lefty stroke that would, one day we hoped, turn Detroit on.

Pena doubled in his first Tigers at-bat — a shot right over the first base bag — and had three hits that day, leading the Tigers to a 9-8 win. The baseball world seemed to be his oyster in Detroit.

Pena watches another baseball go bye-bye; his career almost followed suit

But it wasn’t long before Pena struggled, striking out frighteningly often and the more he failed, the harder he tried. And the harder he tried … well, you get the idea. A 43-119 season with the Tigers in 2003 didn’t help; it only served to prop Pena up as a symbol of what was wrong with the team: another clueless young player wrongly evaluated by an equally clueless Tigers front office.

Well, Pena not only made the (Devil) Rays last season, he busted out: 46 HR, 121 RBI, .282 BA. He still strikes out a lot (142 times in ’07; 31 in 85 AB in ’08), but that’s who he is — and who most HR sluggers are. You take the bad with the good.

The monster year earned Pena a lucrative contract, and maybe — just maybe — he can remove the word “potential” from his vocabulary. I say maybe, because so far in ’08 Pena is hitting just .200 — though he has six HR in 85 AB.

This is the year for Carlos Pena to show us if last year was a fluke, or if he’s destined to be among the most feared sluggers in the next decade. I say the latter is still the best bet. He’ll be 30 in a couple weeks, but while that may be old enough to consider him a late bloomer, it’s right smack in the middle of the start of his prime — if that makes sense.

It’s not outrageous to suggest that Pena may hit some 350 HRs from 2010-2019. Add that to his current total of 138, and suddenly he’ll be knocking on the door of 500 homers. Then what?

Hall of Fame? Gulp.

I’d like to think that Carlos Pena is on his way. He was always a likeable sort, if also maddening to watch at times. We’ll see in a few months.