Old women often dye their hair blond in order to suggest the illusion of youth, whilst some young women like to dye their hair grey because it's a fashion of sorts (for them).
In neither case does the effect really work.
Young-coloured hair on an old woman is what it is - young hair on old. It looks silly and undignified. And as for young women dyeing their hair grey... I just can't imagine what that is all about.
