@Ryudo Prime An Idea I had is a scene of him sitting in a room looking upon World War II with the rest of the Elohim.

So the setting is in 1939/40? And the character is watching WW2?

@Ryudo Prime No, is a flashback

How does he have flashbacks of WW2? Did he use retrocognition? Or did he exist back there?

@Ryudo Prime Remembers back to that point, but I may not do this. But how old should be in actuality/chronologically in the series?

Like I said, older the better. Since it allows the writer to pull of impressive tricks without needing to explain why.

For example:

Your character want to unite every nation and become the sole leader of it.

Q: Why?

A: He had experienced WW2 and therefore he made a deal with angel/demons to gain powers to bring peace by uniting all the nations.

@Ryudo Prime Good Point but he is one of the youngest of the Elohim Side

You can extend the age range brother. Some members have lived for 1,000 yrs and some had only lived for 100 yrs. Or you could also count their age after making a contract with angel or demons.

@Ryudo Prime The Oldest Member is called Jacques Carpenter, his name is a reference to Joseph the Carpenter.

Also I think any of them being a thousand is too much. Like 200, 600 that's fine but 1000, 1050 no

Yeah you are right. 1000 is too much for the writer to put lores in to their existence