It isn't always about the knee, and it isn't always about his age. Sometimes Tim Duncan errs as everyone else does. Sometimes Duncan wants to carry more of the load, to post up as if it were 2003, to score against a sturdy defender such as Kendrick Perkins. Sometimes, such as Thursday, Duncan is stubborn. It's a quality that cuts both ways. Duncan was stubborn during the lockout, too, when he believed he could change his game. He went to a private gym in the Dominion, day after day, working to extend the range of his jumper. Who tries to do that at age 36? The Spurs coaches shake their heads and smile. But they also see what he has gained, because they say just a few feet can alter spacing on the floor. Duncan was at it again Friday during practice, with assistant coach Brett Brown passing to him at the top of the key, with former teammate Sean Marks providing length to shoot over. Duncan attempted shot after shot, the last Spur in a drill, until he finished and walked over for his media session. Wiping sweat off his face with his shirt, he began: "We hope to clean up a lot of what we did yesterday." Cleaning up won't be easy, given the mess. But maybe the easiest fix is Duncan. In some ways, it is about his knee and his age. If Duncan were 26 instead of 36, he would be scoring against Perkins on the block. But Duncan isn't 26. While he can still play defense at a championship level — and Spurs coaches see no drop-off in this series — he has aged as a scorer.