This information was gathered from many different sources, mostly web pages, so I can't vouch for its accuracy. Take it with a grain of salt--good advice for anything you read on the internet, really.
Takehito Koyasu was a "yakyuu shounen" (baseball boy), playing Little League when he was in elementary school, but in the fifth grade, the stability of his world was shattered by the untimely death of his father, and he drifted into juvenile delinquency in junior high school. He says he draws upon his experiences of that time to play his "villain" roles; he thinks that even bad guys must have some reason why they're bad. Eventually, he decided he wanted to become a seiyuu and began voice training. (I think it was Koyasu-san who said he didn't do any extracurricular activities in high school because he was going to seiyuu lessons after school, although I might be thinking of some other famous male seiyuu.) Cold, dark characters still come to him more naturally, but sometimes when he's drawing or writing or thinking about something, he reverts to the innocent happiness of his early childhood.
He attended a Buddhist preschool as a child, and graduated from a technical high school in the data processing division.
Side note: After he became a professional voice actor, Koyasu-san, worried about his image, burned all the photographs of himself in his JD days, even going so far as to collect old photos from his friends. It's actually not an unfounded fear, though, I recently saw a popular singer confronted with old photos of herself in gangster-girl getup on a TV talk show.
Momiage no Himitsu (The Secret of the Eartails)
Why did he grow out his sideburns like that? "I've never answered this in personal profiles or anything, but... It's embarrassing, so I can't say, but... (mumbles) [because] in shoujo manga, the cool guys' [sideburns] were long."
When he's not feeling well (or sometimes in hot weather), he tucks his sideburns behind his ears.
Return to Koyasu Takehito-san ga Daisuki!