User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-83.255.38.101-20111022171157/@comment-76.212.204.92-20111022175307

According to Death, God created Leviathans before angels, so they are at least older than older than normal angels such as Castiel. However, I firmly believe Death meant all angels, including the archangels.