You're right, he's old enough.
I was quite happy when Zidane first retired. He wasn't supposed to play this world cup... and actually I didn't want him to, as I believed some younger players deserved a chance and the way he come back to the team, with all the stories around it, was bad for the team (due to our useless coach who is from Lyon! Bastard! That's because of him that most of our players retired in the first place!). In the beginning it was hell. But then again Zizou's return did help us to get to the final.
Still I thought it was the right moment for him to retire. Even though I know I probably won't see another player like him before a very loooooong time...
Shame he doesn't play for St Etienne now... we could do with a player like him!

So who is going to replace Zagorakis?