[Destiel] The Dadification of One Castiel Novak

When one of Cas' old I.D.'s gets rejected, Sam and Dean tell him afterwards it's because his picture is outdated-but this doesn't make any sense, Castiel explains: Angel vessels don't age.
Dean has to break it to Cas that he doesn't look like he's in his 20's anymore.

Or, the one where Cas realizes he's been in love with Dean this whole time and has been unknowingly choosing to grow old along side him.