Richard Stevenson likes to ride around the kitchen of his Roseburg home in his Jazzy power chair for hours at a time, with a little black cat called Muck seated peacefully on his lap. For a man of his advanced years, Stevenson is pretty healthy, though he does have degenerative heart disease and a pacemaker. His awareness also seems to vary from moment to moment. Stevenson turns 101 today, reaching a milestone he sums up in three words. “That’s pretty old,” he said. On Wednesday, he paused his chair now and again to share a few words about his long …