User blog comment:Ikmeos/Demonic power level, powerful weapons and the primordial siblings./@comment-91.89.184.182-20170227225904/@comment-146.198.136.113-20170228185431

Well, she existed before He did, anyway, so one could link that to age.

Apparently, there is a reference on the Darkness's page about her being older than God and Death:

https://www.youtube.com/watch?v=dg3W2bqpZSE