The age when someone is considered a senior citizen all depends on context.

If you're looking for full retirement benefits, the Social Security Administration will tell you this happens at the age of 67. If you're looking for a discount at Denny's, then senior citizenship starts at 55. And if you're a running back in the NFL, you're considered a senior citizen right when you turn 30.

So when Adrian Peterson -- who just turned 30 this past March -- signed a new three-year, $44 million contract with the Vikings, many began wondering just how much Minnesota would actually be able to get out of their aging back.

With all this being said, which running backs have produced the most prolific NFL seasons in their thirties over the past 15 years, and will any of these performances serve as a guide for what the Vikings might expect out of their All-Pro tailback as he enters his age-30 season this year?