Twenty-seven. Oh, the age of 27. As you might be aware, age 27 gets a lot of attention in fantasy baseball circles, often cited as a “magic” number when a hitter reaches his physical peak and is most likely to break out. It doesn’t take much effort to stumble upon a fantasy writer who discusses this theory, heralding the upcoming season’s crop of age-27ers.

The theory goes that because a player is reaching his physical peak, he is most likely to have a career year during his age-27 season. Unfortunately, most of the support offered for this theory comes in the form of conjecture or anecdotal evidence. I wrote an article last offseason at THT that examined whether age 27 actually is the prime age for breakouts. Unsurprisingly, I found that it wasn’t. Of course, this won’t stop people from continuing to write about it, as they see a player like Rickie Weeks post a 29-home run season in 2010 at the age of 27 and assume that the age is somehow magical. But these people ignore the age-27 players who stumble, such as Adam Lind in 2010, and the players who break out at other ages, such as Jose Bautista at age 29. Anecdotal evidence is never sufficient and can often lead to season-sinking assumptions.

One of the largest causes of this age-27 fallacy, from what I can tell, is the assumed interchangeability of the words “peak” and “breakout.” While both are positive words to hear about a baseball player, they mean very different things. A player’s “peak” is the time when he is in the best shape of his life, which we expect to translate into the best season of his career. A “breakout” is when a player posts better numbers than we expected, independent of physical condition or whether his season is superior to any other the player has or will post.

It’s not incorrect to say that a player’s peak year is generally his age-27 season (there’s some debate about the exact age, but for the sake of simplicity, we’ll say it’s 27). Of course, everyone’s physiology is different, and some will peak at 26 or 28 or 31, but assuming for a moment that the average player peaks at 27, that does not necessarily mean that he’s in store for a breakout at age 27. Take a look at the age curve below, which was developed by Mitchel Lichtman (aka MGL) and posted at The Hardball Times in 2009.

While a player may expected to post his “peak” season around age 27, you can see that the expected gain from his age-26 season is actually quite small. In fact, the age-26 to age-27 jump is the smallest of all age-to-age improvements. If a player only receives maybe a two percent boost in his age-27 season but perhaps an eight percent boost in his age-22 season, why do we think that a player will break out at age 27? When we take a “breakout” to mean a big improvement over previously established levels, it seems downright silly to expect a breakout to occur at the age when players traditionally improve the least.

So while a player may post his best season at age 27, that shouldn’t matter to us if we know what he did in his age-26 season. His improvement at age 27 will be incremental. Yeah, he’ll be at his “peak,” but he was very, very close to his peak last year! If we’re really looking for a player who’s going to “break out,” we’d be wiser to identify quality younger players, who see much larger age-to-age increases in performance. Of course, we have to deal with smaller samples of past performance data with younger players (making it more difficult to say how good they are to begin with), plus all of the prospect hype that tends to inflate their market value, but they’re going to be better bets for big gains than older players are, even when those older players are reaching their peak.

You’re sure to hear a lot of talk over the next couple of months about age-27 players who are ready to explode, but it seems unwise to hope for 2012 breakouts from guys like Brennan Boesch, B.J. Upton, or Drew Stubbs based merely on the fact that they’ll be 27 this season. It might be wiser to focus on younger guys who made their debuts at a young age. With these players, we will have at least a couple of years of major-league data to look at, the prospect hype will have calmed down, and they’ll still be on the most favorable portion of the age curve. Player who might fit that bill this year included Elvis Andrus, Starlin Castro, Jason Heyward, Logan Morrison, Mike Stanton, Jose Tabata, Ruben Tejada, and Justin Upton. That’s not to say that age should be the only thing you take into account when trying to find a breakout, but logic suggests that a young player is a better bet for one than a guy who’s turning 27.