Good article in Running Times featuring 78 year old Ed Whitlock, the first to break 3 hours in a marathon after reaching 70 years of age. Whitlock went on to run 2:54 at age 73!
His training routine has been well documeted- up to 3 hours daily on a 1/3 mile loop around a cemetery. No hills, no speed, stretching, cross-training, or other variations. (No Place to Run)