It's not really a terribly fulfilling answer, doesn't give Castiel too much to work with aside from a rough outline of how long he may have been here - but decades is still quite broad, and if Dean's only going to be giving him one word answers, they're going to get nowhere fast and this already painfully awkward conversation will surely evaporate into strained silence.

Which is fine. Castiel is perfectly content to sit stiffly, quietly, and eat what has been given to him, but he's just so damned curious..

"How old are you?"