Harry Potter Golden Age

Just butting in on the giong grey early/late thing -- I'm a medium/dark blonde, and my mother detected my first grey hair on my 19th birthday. :) I've started dyeing my hair to hide grey rather than for fashion in my early forties.

My paternal grandmoher went from chestnut-brown hair to grey/white in her mid-thirties (although for her, WW II, being widowed and becoming a refugee may have cntributed). My dark-haired father had lots of grey hairs when he died at age 42.

On the other hand, my mother-in-law and her mother, both dark-haired, didn't start going grey until their late 50s and retained traces of their original hair color in their high eighties/mid nineties.

So it's VERY individual, and most likely genetic -- same as human male pattern baldness. (Personally, I prefer to think of Draco with a receding hairline if I must rather than a [possible] comb-over!)