Technically, my very first adventure game was Dizzy on ZX Spectrum, but it's not a pure adventure game so it doesn't count. Later, when my dad got himself a PC, I discovered Star Control 2 which blew me away, left a never fading impression (I still play it from time to time, it became some sort of a tradition) and even seriosly affected my school grades
, but I still don't consider it the first adventure game I played for the same reason, though it's much closer to the adventure games than Dizzy. I think it wasn't until I played LSL 1 that I became aware of the genre, so I consider LSL1 to be the starting point in my adventure gamer's career.
I still remember trying to convince the game that I'm 18. Those were the days...