Like all of us, Frank Gore is getting older. Unlike some of us, Gore isn’t declining with age. In fact, in recent years, Gore … hasn’t changed at all. Today, the 49ers running back turns 30, which, viewed through the prism of his punishing 9-to-5 job, means he’s AARP-eligible. Even before the big 3-Zero, NFL backs can quickly morph from All-Pro to Old-Fogie. Hall-of-Famer Larry Csonka had his last 1,000-yard season when he was 27. Earl Campbell, who is also enshrined in Canton, had his final 1,000-yard campaign at 28. Same with Seattle’s Shaun Alexander, who played in just 27 more games after his 1,880-yard season in 2005. Meanwhile, Gore, at 28 and 29, has produced – almost exactly — like Gore at 26 and 27. Consider the last 1,080 regular-season carries of his career, broken down in 540-carry splits: Since 2011 (ages 28-29): 540 carries, 2,425 yards, 4.5 yards per carry, 16 TDs. From Oct. 26, 2008 to 2010 (ages 25-27): 540 carries, 2,448 yards, 4.5 yards per carry, 15 TDs. It’s quite possible that Gore’s skills are modestly declining, but his production has remained steady thanks to the arrival of Jim Harbaugh and offensive coordinator Greg Roman in 2011. With a more creative offensive scheme, defenses can no longer key on Gore, who suffered through the ill-fated regimes of OCs such as Jim Hostler and Jimmy Raye in his first six seasons.