User blog comment:ImperiexSeed/Death - NOT omniscient/@comment-216.232.39.181-20120809021032

Also

"Since he wrote the Word of God at the beginning of creation he may be older than the Leviathans, although its never stated which creation he was at the beginning of."

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Castiel was just f*cked up by Lucifer when he said the above.

Also

Castiel isn't exactly the most intelligent and "all-knowing" Angel.