To me it seems like the vast majority of dragons probably die by misadventure or violence, not old age.
The oldest dragons are Great Wyrm age. A party of 20th level characters would struggle to take one down. Beings that powerful have a gravity that affects events across countries or continents. There just can't be that many of them in the world. Maybe a handful per species. Maybe.
It makes me think that a lot of wyrmlings are born but only a small number live to adulthood let alone old age. Given that an adult dragon is also a siege engine with legs, they're so obviously adapted for violence, the most likely cause of death for a dragon is probably other dragons.
