I'm bored, so I'll bite.
Something I'm curious about. In your game world, what is the context for Dragons? Specificially....
They no longer exist. If they ever existed at all. A passing memory. Sort of. Maybe. Who knows?
Hard to elaborate on that without spoiling a lot of my game. But, let's say that they exist for the same reason any other monster exists. The same reason magic exists. The island the game takes place on. Do they exist outside of the island? The people who live there can no longer remember. They had words for Dragons before they were shipwrecked on the island, but nobody knows for sure if they ever existed outside of the island.
They know for sure Magic never existed anywhere else in the world, as it's relatively recent even on the island. They know for sure many of the monsters that exist on the island didn't exist anywhere else, as records indicate that many of them are entirely new and didn't even have legends associated with them (like sentient slime puddles!). Diary entries from the first people shipwrecked essentially list monsters that they named or ran across that they'd never seen before. Some old legends from before the island talk of creatures like Elves and Dragons and Chimera. But, were they ever real outside of the island?
Who knows? Hard to say.
Are Dragons immortal creatures, or at least pre-dating other sentient life?
Nope. Very much not immortal. In fact, by the time the game takes place, the Legends of the island state that they'd been hunted to extinction. That is... if they ever existed at all and weren't mere tails of fancy and derring-do. Their legends predate the Island. Do the creatures themselves predate humanity? Who knows?
Or were they created somehow through magic?
It's hard to explain. From a narrative perspective, nobody knows where they came from. From a "behind the scenes" perspective... They existed before Magic did. Though, they were created by the same thing Magic is being created by. Along with... lots of other things...
Or, did they evolve naturally just like other biological creatures?
None of the creatures of The Island were evolved. Several aren't even biological in nature. They just... exist.
-Are they evil, neutral, or good?
They're just animals. Just like any other creature. They hoard shiny things 'cause the shimmer attracts their eyes and helps them also attract mates. Sort of like those birds that just collect blue things to attract a mate. Dragons just collect anything that shines. They eat when hungry, sleep when tired, and defend themselves if adventurers come into their dens.
Dragons also notably put their shiny stuff at the entrance to their caves. Because... well... can't attract mates if they can't see it.
-For the very large powerful dragons, why do they stay within their caves and dens, and not go out and wreak havoc and destruction upon the world?
They don't consider it "wreaking havoc". They just go out and eat smaller animals when hungry. They don't really burn things down or kill people if they can avoid doing so. Claws, Breath, and Tail are used primarily in self-defense. Though, there have been recorded cases of "mad dragons" that just went crazy and attacked anyone and everyone. They lack the sense to stay alive very long, however. They're more akin to animals who have gotten rabies.
As for why they stay in their dens... Well, it's safe in there. It's also a good place to raise a family, where other predators might fear to tread. If they perched atop a mountain or castle, some birds or other animals might try to eat their babies or their eggs.