"I shouldn't think so," is the only reply he gives at first. It's not an admission that he understands how Lucius feels in his own particular anomalous state - because he doesn't. But he does sympathize. He's acutely aware of their shared relative strangeness to the others.

He isn't certain how to express just what he's feeling about this, or what he hopes to gain by trying to commiserate with the man opposite him - and then, how to phrase it under the carefully guarded parameters begged by a conversation with Lucius Malfoy. Subtlety is a complicated thing on occasion. So after a moment, he simply goes on thoughtfully, "It does leave one feeling particularly old."

Severus says the word 'old' as though it's a completely foreign and insulting concept. He's only thirty-eight (or forty-one), and wizards have such long natural lives. How dare old age come creeping around the corners of his life this way. This soon.