When do most girls/women start to see gray hair?

I'm a 21 year old girl and I am constantly worrying about getting gray hair. At what age do most people notice gray hair? A friend of mine is my age and he already has many stray's. I don't know if there is a difference between male and female gray hair...When do most girls/women start to see gray hair?
I have had gray hairs since I was 18. Not noticable for anyone else to see but it's thereWhen do most girls/women start to see gray hair?
its different for every girl, and the level of stress. average - mid to late 30s. I was 12 when I got my first gray hair. Maybe thats because I had a mother load of stress, and I have delicate hair - its dark red with a hint of brown. and my gray hairs are silver! xD
i think at about the age of 45. my mom is 42 and she doesn't havea any gray hair yet.
SOme people get in earlier form things like genetics and stress! Dont worry! My sis has it and she is 33 my dad had it since he was 20 reaaly just wait and see!