I couldn't agree more.
It make no sense to me why anyone would want to contemplate that it is time for Zanetti to retire or be replaced just because of his age. Come on, even at the "ripe old age ( football wise )" of 38, he is still as fit as any other players still playing that are much younger, and rarely gets injured despite playing full 90mins week in week out. After watching the Siena game, I am 100% convinced that our beloved Capitano can easily play another 2 to 3 seasons or perhaps more. The measure of keeping a player should be on performance. When he made those runs and skip pass defenders like they weren't there, or when he made those fabulous tackles to win back the ball, that's the working of a player as fit as any player in his 20s but with a 20+ years of football experience backing it up. That is something that you cannot buy with money.
A heir should be groomed to replace the Capitano when he eventually retires, but I doubt the footballing world will see another Zanetti anytime soon.