How long do the dragons of Middle Earth live?

Question

Do the Dragons of Tolkien's works die a natural death, or are they like the elves and can only be killed in battle?

Answer 1

Thorin's speech at the beginning of The Hobbit suggests that it might be possible for dragons to die a natural death:

"Dragons steal gold and jewels, you know, from men and elves and dwarves, wherever they can find them; and they guard their plunder for as long as they live (which is practically for ever, unless they are killed)..."

On the other hand, that could just mean that it's possible so far as Thorin knows. Tolkien never actually writes about a dragon who dies of old age. Certainly Smaug's boasting suggests that dragons get stronger as they age:

I laid low the warriors of old and their like is not in the world today. Then I was but young and tender. Now I am old and strong, strong, strong!