Truth be told, and I have some experience on this, you can become "old" overnight, or it seems like it. You can tell in the legs. One day, that springy first step is more of an anvil shove. While most of the players listed above are in their early thirties, some of them, not all, are going to start looking slow. It is why GM's are always harping on getting younger. It is why they are also always talking about having to win NOW, as many of these guys get quoted as saying right after they make a mega-trade.
The NBA is a young man's game, and it is always interesting in watching how players like Jason Kidd and Grant Hill learn to compensate for their aging bodies. With big men, it is different, since few have the Garnett/Duncan gifts of speed AND size. They lose speed, who notices? But the PG, SG, and SF's out there who rely on speed can burn out big time.