I don't dye my hair often because of the cost and I don't enjoy spending the time on it. I'm not good at keeping up with the roots. Also mine always fades/bleaches easily.
I have an aunt who started going grey when she was a teenager and was completely grey by the time she graduated from highschool. When she was young she dyed it black or dark brown. Then later would dye it blond. I think if I had been in her situation dying it would have been much more important to me.
I had one grandmother who always dyed her hair but had the typical granny hair cut and curl. She didn't really look younger. She just looked old with brown hair.
I had another grandmother who didn't dye her hair, but kept more youthful hair styles and longer hair. She didn't look young, she just looked old with glamorous hair.
They both looked just fine. Neither of them fooled anyone, but both of them were happy with their outcomes.
I'm in my forties, and I have enough grey it's noticable. I often debate about it. I don't like the hassle but I don't want my appearance to have a negative effect on my life either.
My hair doesn't hold hair color well. It fades. Even when I have dyed it darker brown or black, it fades to a lighter shade than my natural color is.
When I was a little girl I had a Barbie coloring book, and I colored a girl's hair light blue. I thought it looked pretty and I asked my mother if people could have blue hair. She thought I was silly and said that no one would and if they did no one would like it. I felt sad over that. Now lots of people are using all kinds of colors and it's a trendy thing.
I have thought about trying ash brown and maybe some lighter ash highlights. I would have to go to a salon though because I'm just not good at this type of thing, and then I consider the cost again.
Is it vanity? I don't know. I think it could vary by person.