First of all, the layout. Main image features Alucard from Castlevania: Symphony of the Night. Actually, Alucard is pale gold blonde, and I'm perfectly aware of that. However, he was white-haired on first image of him that I saw - low quality jpg to blame - and somehow it got to my mind that he looks better with snowy hair.
Alucard and Castlevania are c. Konami. Artwork by Ayami Kojima.

White hair does not necessarily mean white/gray with age. Absolutely not. Apart from albinos, there are many characters with snowy heads from literature and movies. Starting from Sephiroth (Final Fantasy) starring in computer games, to infamous Elric of Melnibone and Raistlin Majere, fantasy literature characters. And there are lots of them in manga.
Generally, white-haired people are not... good. Or at least not 100% good. They don't need to be evil either; it's just dark mystery dwelling in their past, and something in their eyes makes one think of correlation of life and death, sense of existence, and other philosophical matters.
White hair are unnatural, mystical. They make people outcasts, loners, weirdos. Great intelligence, too, yet not for pro-society use. Eerie.
(That's what I think about white hair, at least.)