Six months for full maturity, and almost forever, as well as give "riders" prolonged lives, I took the prolonged life from Eragon.
How big are they, too. Are they the small kind of 15 feet, the average in mythology of 100 feet, or Smaug sized, 300 feet?
I was hoping that or the Dragonlance version where you suck out the spirit (personality) leaving the opponent wandering around aimlessly.