Brown was 29 when he played his final snap, then retired while still dominant. He had the right idea.
Very few backs have remained productive into their 30s. The chart below shows running backs from current NFC West franchises who carried at least 50 times in a season past age 31, according to Pro Football Reference. I limited the search to the past 35 seasons (the newest current NFC West franchise, Seattle, entered the NFL in 1976).
It's a short list featuring seven players, including three legends finishing their careers wearing unfamiliar uniforms (Emmitt Smith in Arizona, O.J. Simpson in San Francisco and Franco Harris in Seattle).
None gained 1,000 yards in a season even though all played in the 16-game schedule era -- an era Brown ridiculed for this marvelous 1983 Sports Illustrated piece discussing his comeback threat. In it, Brown said Harris might break his record if he kept running out of bounds frequently enough to prolong his career. The best quote from Brown, by far, makes me wonder what Brown must think of the current NFL game:
"Where has the danger in the game gone? I can't accept quarterbacks sliding and running backs running out of bounds. Ever since the merger in 1966 and the creation of the Super Bowl, the owners have been more concerned with ratings than the level of the game. Coaches put up with players waving into TV cameras, giving high fives and spiking the ball. That sells. The Monday Night Football broadcasters have become bigger than the game. Who is kidding whom? Who's to say a 47-year-old can't do it? I'm not talking about being Jim Brown of 1965. I'm talking about being Jim Brown of 1984. If Franco Harris is gonna creep to my record, I might as well come back and creep, too."
Barber, for the record, ranks 22nd on the NFL's all-time rushing list. He's within 200 yards of passing Watters for the 20th spot. Watters rushed for 1,242 yards at age 31 and still appeared to have quite a bit left, but the Seahawks had drafted Shaun Alexander and Watters wasn't interested in a situational role.
RB Watch: Top Performances Past Age 31
Since 1976, for players on teams currently affiliated with the NFC West.