Breaking down 30-year-old running backs

One thing I can tell you with confidence: Edgerrin James will not be on any of my fantasy football teams this season.

Why not, you might ask?

It's simple, really: He'll turn 30 years old on Aug. 1, and with 2,849 career carries, he has more than all but one player in NFL history had at the time of his 30th birthday (Emmitt Smith had 65 more when that 30th candle hit his birthday cake).

That might not seem especially disheartening, and, in fact, my declaration might take you aback, considering I'm rarely the type to buy into the age-old, widely-assumed theories of fantasy sports -- at least not without the statistical evidence to back them up.

Well, I've run the numbers, and I've rarely seen a theory in sports that has stronger statistical evidence than this one: NFL running backs hit a wall once they turn 30. Nay, they hit a concrete wall, and it practically stops them flat.

If you don't believe me, feel free to call Shaun Alexander and ask his opinion. Don't worry, I'll wait patiently for you to get back. In all of our game's history, I don't think I've seen a stronger example of what can happen to a running back after he turns 30 years old than Alexander. His scrimmage yards per game dipped by 33.5 from 2006 to 2007 -- and his age-29 year of 2006 wasn't great to begin with -- and since 2005, he has lost 23 total touchdowns from his season-ending stat line. That's a steep decline.

Folks, if there's to be an "Alexander of 2008," it might just be James.

Consider that in his two years in the desert, he has averaged 74.4 rushing yards, 87.6 scrimmage yards and 0.41 total touchdowns per game. That's down markedly from his final three years in Indianapolis, when those numbers were 98.0, 123.3 and 0.77.

History doesn't provide him a strong endorsement, either.

Being an only-statistics-support-theories type of guy, I compiled the career statistics of each of the top 50 players in NFL history in terms of rushing yards, to prove that 30-year-olds indeed have it rougher than younger players. Further breaking down their yearly numbers by their ages as of Sept. 1 in each season, then averaging the total numbers to a 16-game NFL season, here's what the average player from the group did by age:

In particular, look at the level of touchdown production. Those all-time great running backs lost 20.4 percent of their touchdown production from their age-29 to age-30 seasons. Then, they lost another 13.7 percent from their age-30 to age-31 seasons and 11.9 percent more from age 31 to age 32. In a matter of three years, from their age-29 through age-32 seasons, history's greatest running backs lost 39.5 percent of their touchdown production, and that's assuming they didn't retire before turning 32 (as Jim Brown, Eddie George and Barry Sanders did).

In addition, those 50 running backs lost at least 10 percent of their scrimmage-yard production each year beginning with their age-30 season (13.1 from age 29 to 30, 13.2 from 30 to 31, 17.3 from 31 to 32 and 18.0 from 32 to 33, to be precise).

Those are some staggering drop-offs, wouldn't you say?

Not that I'm foolish enough to think that any two running backs age the same, perform the same or possess the same track record in the health department, but when looking at numbers like those, it's tough not to be a bit more hesitant about James and his "ancient" brethren. Besides, in James' case, he's facing a double-whammy: The age-30 threshold as well as one of the heftiest workloads of any player through this stage of his career.

Speaking of those "ancient" brethren, though, take a look at some of the other notable running backs who will kick off 2008 aged 30 or older (as of Sept. 1):

Age 30: Reuben Droughns, James, Thomas Jones (1,659 career carries) and Kenny Watson
Age 31: Shaun Alexander (2,176), Ahman Green (1,941), Sammy Morris and Ricky Williams (1,763)
Age 32: Kevin Faulk, Aaron Stecker and Fred Taylor (2,285)
Age 33: Warrick Dunn and Michael Pittman

But enough with the negative, here's the tasty tidbit that chart reveals: History's best running backs tend to hit their physical peak in their ages 25 through 27 seasons. And what's their most likely age for a breakout season? It's either their age-24, from a scrimmage-yards standpoint (14.7-percent boost), or age-25, from a total touchdowns angle (13.7-percent increase). Boy will that come as good news to those keeper-league owners who have been hoarding DeAngelo Williams (now 25) all these years. It might be the one saving grace he has towards avoiding "never-gonna-be" status.

Here's a rundown of key running backs now at those "prime-year" ages:

Age 24: Lorenzo Booker, Michael Bush, Brian Leonard, Garrett Wolfe and Selvin Young
Age 25: Joseph Addai, Marion Barber, Cedric Benson, Frank Gore, Ryan Grant, Steven Jackson, Jerious Norwood and Williams
Age 26: Ronnie Brown, Andre Hall, Brandon Jacobs, Willis McGahee, Michael Turner, Leon Washington and Cadillac Williams
Age 27: Tatum Bell, Chris Brown, T.J. Duckett, Fred Jackson, Julius Jones, Willie Parker and Clinton Portis

Suddenly, even the rehabbing Ronnie Brown is looking like a little more appealing draft pick than Mr. James...

Tristan H. Cockcroft covers fantasy sports for ESPN.com. You can e-mail him here.