Adrian Peterson's future with the Minnesota Vikings is in doubt, but he wants to play for at least another half-decade.

"People say, 'Oh, running back hits 34, 35 (and he's done). When you get to 30, you go down.' I don't believe that," Peterson recently told USA TODAY Sports' Tom Pelissero. "I believe I'm just now here in my prime. I believe these next five or six years -- or however long I decide to play -- it's going to be the same production and I'm going to do even better than I did before in my 20s."

Peterson turns 30 in March. Studies have shown that running-back production decreases by 15 percent at age 28, 25 percent at age 29 and 40 percent by the age-30 wall.