As we now exist in an age where every game imaginable has age ratings - as well as specific sites that evaluate how appropriate specific video games are - it's hard to imagine the "Wild West" days of the industry before these classifications emerged.
The idea of not having some source to rely on - telling you how potentially traumatising a game could be - is impractical for a whole load of reasons. You don't want to accidentally hand Manhunt to a child and make them scared of pigs forever.
While some ratings did exist, they were generally self-imposed ones, given to the game by its own publisher. This was an issue because, naturally, publishers rated their own games for lower ages than they should have, in order to increase a potential customer base. The sketchy nature of this setup went under the radar for some time, until one infamous game: Night Trap.
A game about controlling security cameras in a bid to save various young women from home invaders, Night Trap was by no means the first mature game in history, but what set it apart from titles of a similar ilk was one crucial detail: It used actual filmed camera footage.
While games like Leisure Suit Larry got away with lude hijinks because they were in "cartoony", pixel graphics, Night Trap was recorded much like you would a film, adding a layer of realism that would come back to bite it after launch.