I think most of us know this by now: A 21-year-old rookie with the same batting statistics as a 25-year-old rookie will almost always go on to have a much longer, productive career than the 25-year-old. Likewise, we assume a 23-year-old has more potential to improve than a 26-year-old, who has already reached the age that most players peak.

Because of this, Jay Bruce is a popular breakout candidate for 2011. He was 23 years old last season, has three major league seasons under his belt, has the prospect pedigree, and just feels like a guy ready to take one final leap to stardom. I'm on that bandwagon: I do a feel a monster season coming on for Cincinnati’s 24-year-old right fielder.

Even though the Reds won the NL Central, Bruce's 2010 campaign (.281/.353/.493, 25 home runs, great defense that Baseball Prospectus rated as the best in the majors for any outfielder) fell under the radar for several reasons:

(A)He hadn’t been very good in 2009, when he hit just .223 and then suffered a broken wrist;

(B)He got off to a slow start (.266/.339/.446 with 36 RBIs in the first half);

(C)Joey Votto was, you know, getting a lot of attention.

In the second half everything clicked, perhaps in part because Bruce's wrist was 100 percent. In 210 plate appearances, he hit .306/.376/.575 with 15 home runs. You can do the math and triple those numbers to approximate a full season of PAs and understand why some believe Bruce could hit 35 homers, score close to 100 runs and drive in 100-plus. Factor in that he’s still young, has big-time tools (he was once Baseball America’s No. 1 overall prospect), is more than a year removed from the broken wrist and showed a small spike in his walk rate, and he looks like a player who will improve.

That’s my belief; I think he’s a good bet for fantasy players and a good bet to make Reds fans happier than a basset hound running on a beach. But -- yes, there is a "but" here -- there’s something else in play. Even though the axiom is that young players improve and that hitters generally peak at around 26 to 28, it’s possible that Bruce has already reached his peak ability. Just because he’s 23 and has areas that he could improve doesn’t mean he will improve.

I checked out the 20 best 23-year-old hitters over the past 10 seasons (minimum 502 plate appearances, using OPS+ from Baseball-Reference.com). Bruce ranks 12th on that list with the 127 OPS+ he registered in 2010. The guys on this were already good hitters at 23, so we’re asking: How much better do they get?

The answer, at least with this group: Not much. Hitters ranging from Albert Pujols to Miguel Cabrera to Joe Mauer to David Wright to Nick Markakis were essentially fully developed hitters by 23.

Here’s the chart:

This isn’t to suggest all 23-year-olds won’t improve (such as Carlos Gonzalez making a big leap last season at 24); it’s a possible indicator that if you’re talented enough to reach the majors at 21 like most of these guys and already an excellent hitter by 23, you may not improve much more. Bruce has shown steady progress since his debut in 2008, but he also had a high .334 average on balls in play last year. It's possible he'll regress back to his .299 career average. It's why Baseball Prospectus projects Bruce to essentially repeat his 2010 numbers: .269/.339/.482.

I'll still hold out for a leap -- more walks, fewer strikeouts, 30-plus homers -- and fans of Colby Rasmus and Andrew McCutchen are surely expecting a similar leap. Maybe the wrist injury did hold him back early in 2010, but it’s possible Bruce will settle in as a very good player and potential Gold Glover, albeit not quite a perennial All-Star type.

Final note: It's possible, of course, that PED usage may have some unknown influence on the above results. I'll do a future post to look at a wider swath of good 23-year-old hitters going back more years.

Follow David Schoenfield on Twitter at @dschoenfield. Follow the SweetSpot blog at @espn_sweet_spot.