Kaladze is only 27 or something. But you are right, Milan were idiots to buy Stam. Not only did it screw up their 4-3-1-2 tactic, now they must rejuvenate their entire defense next summer.
What he's actually saying is that he will quit this summer if gets relegated to the bench. Which is only fair in my opinion, he has played for more then 20 years in the first team after all.