Scoring 40 points on only 16 shots is an amazing feat at any age. The question with older players like Pierce is whether they have the legs to come up big at the end of a grueling playoff series.
Against Lebron in 2008 when Pierce was younger, he did. Last winter, he didn't. It's conjecture whether PP didn't have the legs because he played too many minutes that season, or just had gotten old.
Father Time spares no one, unfortunately. If Pierce can turn a game 7 performance this winter like he did to the Cavs in 2008, that would show that he's not too old.