Immortality

Immortality
Celestia and Luna are the only two beings alive who know the spell used to grant immortality. While those awarded with the effects of the spell will be immune to the effects of age, they can still be killed by any other means. Celestia and Luna are very, very particular about who they award immortality to. Since the spell's discovery, they have only awarded it to those who have served Equestria, or the world, "above and beyond the call of duty."

The average lifespan of a pony is 70-100 years. Young ponies stop growing around the age of 18.