If the Avs are scared of paying a defenceman at 33, then they're never going to sign anyone.
Phaneuf is getting paid until he is 35.
Bouwmeester is getting paid until he is 35.
Keith until he is 39.
Campbell until he is 36.
Suter until he is 40.
Enstrom until he is 33.
Weber until he is 40.
Carle until he is 34
Wisniewski until he is 33.
Wideman until he is 34.
Chara, Boyle, and Timonen's last contracts all took them to over 35.
A #1/2 defenceman isn't going to become a UFA at 26 and sign a discounted deal with the Avs. If they want a good defenceman, they're going to have to come to terms with the fact that they will be paying him on the decline.
Pretty much all of them are a different player type than Girardi.
Girardi is more like Volchenkov, Orpik, Sarich, Scuderi and Mitchell. Those kind of defenders don't have the same durability as others. They don't have good enough skating to stay effective when they lose a step or two.
Same goes for Callahan. He's not going to be able to play well at 36 while a player like Selänne or Whitney will be able to without problems.
That said, Girardi will just be 30 this summer, so it's possible he'll have 3-4 good years left in him. It's hard to know. He's not had injury problems in the past, which is a plus. It'd be worse if he had knee or shoulder problems previously.