What if magic has always existed since the beginning of time and the gods were originally normal humans who through ley lines or naturally occurring places of immense magical energy were exposed to more magic than any other being could ever dream of possessing. And this immense magic made them immortal this turning them into 'gods'. But they began to abuse their power and because of their immortality they began to upset the balance of nature. And now that's why Nature would never allow any one else to truly be immortal there's now always a loophole.