Dragon's legacy had been a long one, he had appeared countless times through the time, and each time, someone ended up sealing him one way or another. Though such means were never deployed since the start.
The world in the golden age believed it could take out this evil serpent, and it did until it somehow recovered and came back stronger than before, which is how the serpent earned the title of Immortal.
As for how old this serpent was? Only a few among the Totems knew of this truth. The majority of them live with frustration over its existence while they wait for when the serpent will rise again and wreak havoc once again in the world.
And once this serpent did something like this, the Totems were dispatched to deal with this issue. With the one from Cynark being an Angel as well.