Frank Gore is 29 years old and has been the featured back of the 49ers since 2006. Steven Jackson turns the same age in three weeks, and has been beaten and bruised while playing on bad teams his whole career. Michael Turner had his 30th birthday in February, and has accumulated 300 carries in three of the last four years. Fred Jackson (31) and Willis McGahee (31 in October) have had varying degrees of wear and tear during their careers, and are both competing with younger backs on their roster.

We know the wheels will fall off for these players. But do we know when? And how severe the drop-off will be? Each running back is unique, with his own genetics, history, and supporting cast. It’s difficult to find true comparisons to any one running back, let alone a group of runners. Still, we can try to identify the general aging pattern of top tier running backs.

I looked at all running backs who entered the league in 1990 or later, rushed for at least 5,000 rushing yards, averaged at least 40 rushing yards per game for their careers, and are retired. There were 36 such running backs.

Now we need a metric to measure running back productivity. Generally, I don’t think people worry about running backs failing to be factors in the passing game as they age; Kevin Faulk set a career high in receiving yards at age 32. I don’t think the focus is on touchdown production, either, and we all remember Jerome Bettis still being a short-yardage force even when he was well past his prime. No, when people discuss running backs hitting a wall and deteriorating, the focus is on declining rushing yards and rushing yards per carry. One metric I’ve used before is called “Rushing Yards Over 2.0 Yards Per Carry” or RYO2.0, for short. As the name implies, a running back gets credit for his yards gained over 2.0 yards per carry, so 300 carries for 1000 yards is worth 400 marginal yards, as is 1,060 yards on 330 carries. Essentially, we’re looking at just rushing yards with a small adjustment depending on the player’s yards per carry average.

I calculated the RYO2.0 for each of the 36 running backs at ages 22 through 34. The red line represents the average RYO2.0 for the group at each age for all 36 backs; the green line represents the average RYO2.0 only for those backs who were active in the league at that age.

Running Back production by age