I’ve been going grey for as long as I can remember. I was in my teens.
I am shocked by the poll results, I thought most would be in the late 20s or early 30s
31, none yet. I keep thinking I see one, but when I get a close look, it always turns out to be just a very blond hair. (My hair is a sort of dark blond/light brown color, but the flyaway hairs at the front tend to be lighter.)
I’m 29 and I just started noticing a few within the last few months. I’ve been dyeing my hair since I was 16, though, so I have no idea how long they’ve actually been grey without my noticing.
I was getting my hair cut on my wedding day and we noticed the first one.
I’ve got a handful in one spot. I’m hoping I get a stripe. They’re kinda buried under the other hair so you can only find them if you’re looking in the right spot.
I’m probably the only one who is looking forward to it - I would love to have all white hair, but, if my dad is any guide, I probably won’t get to that point until my 50s. I’m almost 30 now.
It’s funny how some people see a grey hair and immediately start dying it while others look forward to the prospect.
If ‘Under my chin’ is included as ‘on my head’, well…
In college, I was walking with a roommate and she reached over to pull one of her very long, blond hairs off my chin, as it had apparantly wafted off her head and stuck to mine.
It was stuck alright. It was a white hair, at least 6 inches long, and quite well attached to a follicle under my chin.
Neither one of us had any fricking idea how it grew that fast, cause it sure hadn’t been there very long. SOMEone would have noticed!
Aside from that, not sure when mine started going grey, as I have dyed it various and sundry colours for 25 years. But I first noticed these neat ‘highlights’ in my hair about a year ago. (Edit-at 42) Bright fracking silver highlights. I confess, I pull them. =p If/when the majority starts going that colour, I’ll just HAVE to let it grow out natural to see what it looks like!!
Then I’ll likely dye it back to auburn. 
Young teens. Had a Mallen streak / Dickie Davis thing going on (British Dopers of a certain age will get the reference, for others there is Google).
Earned me the nickname ‘Badger’ and even I had to admit that when catching a glimpse of myself on a shop’s CCTV monitor, it looked a bit like a bird had just shat on my head.
Nothin’ yet. 38 years old, dirty blond hair. My mother tells me I have the same hair as her father, and it turned a nice shade of silver when he was in his 50s. Fine by me!
I only look forward to it if it stays distributed as it is, or my temples get in on the action…or a cascade starts and I go completely white really fast.
I do not relish the idea of spending many years with grey shot through an otherwise brown pate randomly.