I recently devised a thought experiment that involves an adult dragon that has the ability to cast the haste spell and has the polymorph self special ability. The dragon would transform into an elf and then cast haste on themselves. The dragon would age 5 years due to the side effect of the haste spell. The dragon would repeat the process each day until they reach the venerable age category. Even assuming they only cast haste once per day it will take less than a year for the dragon to become venerable. The dragon would then breed with another dragon and then cast haste on their children each day to rapidly grow them into intelligent adults, and eventually venerable dragons.
Assuming a large community of dragons decided to do this, dragons would be able to conquer the world with an army of invulnerable, shapeshifting venerable dragons. Even if they didn’t want to use direct force to conquer the world, they could infiltrate society by polymorphing into rulers and other important people.
So my question is: how would the human and demi-human civilizations of the world counter such an attack or would everyone be enslaved by dragons in a couple years?
Venerable dragons spend 90% of their time in their lairs, apparently sleeping a years at a time. I don’t think they’d muster the energy to conquer the world…
If they did, an enterprising group of adventurers could threaten them with a viral army of spectral dragons: Get a necromancer to control a spectre. Have that spectre kill a dragon – you get a spectral dragon. Unlesh it with the command to make war on dragons, creating more spectral dragons making war on dragons. Eat popcorn while the world burns.
A less messy option would be to devise a ritual to penetrate the fourth wall and call shenigans on the Judge. 
Dragons are innately magical beings and don’t suffer mortal side effects such as being aged by haste spells.
dragons and popcorn, now im hungry