User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-5619706-20121108182206/@comment-5110811-20121203221542

Cas was a newly appointed Seraph. Even with his upgrade, he's nothing compared to Naomi or Zachariah. We don't know if he had all of heaven's weapons with him past Season 6. Since you said it your self, we can't take Castiel and Death's word bit by bit. But they do contradict each other. Cas implied that Metatron is older than the leviathans. We now know that Metatron is a confirmed archangel. We just don't know if he's older than Michael and Lucifer or younger. Cas's statement makes Death implying that the Leviathans are older than angels, but not the top archangels.

If Metatron is younger than Mike and Lucy, then the top archangels are older than the leviathans. If he is older, then he is the only angel that's older than the leviathans.