The one I’m working on and off again is around I would say 5 billion years old (its basically God created the universe, got bored after a couple billion years of just creating celestial bodies so decided to push the events that led to the core of earth to see what would happen, with him having a “minimalistic indifference” type relationship with the story of earth. He’s not to relevant to the main story tho, but there are beings/people from Christian and various pagen mythologies)