User blog comment:Jade25/How did Eve get here?/@comment-3481504-20120415232025

Possess no knowledge on that, as the show gave not such designation. Although, I do know:

She's at least older than angels, ones such as Cas, however I'm a bit doubtful if this also applies to Seraphs.

Samuel describes his first appearance as being here 10,000 years old, but that still doesn't answer how she came to be.