Why did obama go gray so fast?

Hard job: To the extent that grey hair start is due to stress and the difficulty of a job, obama has the toughest job on the planet. This may have contributed to his seemingly premature or rapid onset greyness.

Stress Depigmentatio: Stress can lead to earlier depigmentation of hair that is already genetically predisposed to graying. However, in general, hair loss is more associated with stress than hair graying.