Dean kinda doubted that he couldn't imagine, but he knew what she meant. Most people probably couldn't imagine.
Sam used to see the future. For a while. He had a dream about Jess weeks before she died. It went with the demon blood. For a second, Dean wondered how old Faith was. Was a Slayer just another one of Azazel's 'special' kids? Was that one of the variations? He didn't think so, but he also didn't know. If she was Sam's age...
He let it go, for now. Something else to ask Bobby.