My Dad was totally gray at 30 but my Mother is 71 and has just in the past few years turned completely gray. Both my sisters would have white hair if they didn't color it (like Daddy) but I have a silver streak that starts at the left temple and goes across the top of my head like Mama. My younger sister let her gray grow out a few years ago and kept it that way for about 3 years. I can't do it. Gotta keep 'em covered up.
Mama has never colored her hair and she's a retired hairdresser.