Crazy range! I am 49 and have just a few strands so far, but my younger sister (46) has darker hair and considerably more gray.

Mid 20s. Dying regularly by my late 20s. Let my gray grow in at 43. Im 49 now and my hair is silver leading to white.

Age 18

Usually the lighter your hair complexion/color, the earlier you start.
Usually.
Some very light blonde people start going gray in their mid 20s are completely gray/white by their 40s.
Some dark haired people don't start until their late 50s and don't go gray until their late 60s or 70s.

48 on my temples and roots

In my mid 20's.

Had to color regularly since just before I turned 40. It’s taken over in the past few years, ugh, and I’m too young in my early 40s to go gray so I’m at the hair salon every 6 weeks.

55 and just have some grey in the sideburns and a few strands on top. Blonde highlights make it hard to notice. I’m surprised it’s not more grey.

Noticeably from age 35.

46 and I have a noticeable grey streak at my left temple, but none other than that.

42 the grays started. 45 now and they are still sparse enough that I think I’m the only one who notices but I know they are up there plotting to take over.

52 and I have a noticeable streak. No grey beyond that. The streak started slowly in my late 40s. I'm keeping it and seeing how it develops.

53.

Around 34 I had white "sideburns" I used to cut short. By 40 I had those and a white streak at my side part.
Started coloring.
Let it go feral during covid when I was 70. Such a freedom not to have to sit in chemicals every 4 weeks or have roots. I am 74 and mostly gray, a nice range of white to dark silver.

Question in topic. I mean more when was it noticeable, not when you saw your first strand or two.