Well it's pretty obvious that the Old Ones were on earth way before "The Five" so the real question is where the Old Ones came from. My personal thoughts are that the Old Ones are aliens, but that would be too easy an explanation. So I chose to speculate that the Old Ones are beings created from all the bad traits humans have (greed, jealousy, etc.

) and that "The Five" are people that have been altered by the good things about humans (love, hope, etc.

) in order to defeat the Old Ones. Of course I'm not the author so I have no idea if my thoughts are accurate.

Hope you can accept my answer.