The idea of white hair not related to age is a common enough trope marking a character as mystical, pure, aristocratic, cruel and/or unstable in literature.
For example, Elric, the antihero protagonist created by Michael Moorcook seems to be a clear prototype for Fulgrim. The last emperor of the ancient Melnibone civilization, he is an accomplished sorcerer and albino. Elric uses ancient pacts and agreements with demons to aid him and also wields a possessed black blade called Stormbringer that feeds on souls and is destined to destroy him.
Another example is the Targaryens from R.R. Martin's Game of Thrones. The Targaryens are the deposed rulers of Westeros and tend to have silver-blond hair as well as violet eyes. Their rise and fall was closely associated with their mystical control over dragons.
The trope is also very common in anime and video games. Sephiroth of the Final Fantasy series is a white haired villain who has been endowed with cosmic powers as a result of a megacorporation injecting him with cells from an extraterrestrial lifeform. He is considered one of the most beloved video game characters by many of the fans of the series.
In comics, Magento is a silver haired proponent of mutant superiority whose role has varied from supervillain to anti hero to superhero. His ability to generate and control and generate magnetic fields and closed fist politics make him one of the most powerful and compelling characters of the X-men comic books. While he is considered to be old enough to have lived through WWII, his hair color is considered to be genetic as it has not changed with age and is also a distinguishing characteristic of his son, Quicksilver.
In films, characters such as Prince Nuada from Hellboy 2 and Roy Batty from Blade Runner also stand out as notable tragic, charismatic white haired male characters with dark futures.