Now that Frank Gore is 30, how much does he have left?

Daily 49ers blog for NBC Bay Area website: With Frank Gore's 30th birthday today, many wonder how much longer he can continue to be productive. For most NFL running backs, 30 is the 'invisible barrier' that many can't break through. http://www.nbcbayarea.com/news/sports/Gore-Hits-Age-30-the-Invisible-Barrier-for-NFL-Running-Backs-207382161.html