First 18+ game? Eternal Darkness, shortly after it was released I rented it, nearly soiled myself during some of the insanity freak-outs, especially the memory card one. Of course, I was nowhere near 18 at the time, but once you're addicted to horror, there's no turning back. Eternal Darkness was a gateway drug, the next year I upgraded to Silent Hill 2 and will never be the same again.