At the age of late 16 / almost 17. Here is my answer from a similar post in another Sierra-related forum:
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I remember the first time I saw Larry -- the summer of 1988. My brother was at the local ball fields for a Little League game, so I took the car to a friend's house near the game.
My buddy was the type of kid who was really into computers and modems/BBSs. While helping the local bank get rid of viruses, he would collect and store them on 5-1/4" floppies... just in case he needed to use them (!).
Anyway, he showed me Leisure Suit Larry In The Land Of The Lounge Lizards on his PC Clone. Not having a PC myself at the time (I'd have to wait until my Freshman year in college -- the CoCo would have to suffice for my Senior year in high school), I was amazed by the game. We must have played through at least half of it before I had to pick up my brother...
Got a copy of it in my Sophomore year in college from a friend who was a huge Sierra fan. He had an original Tandy 1000 machine back in the mid-'80s, and as such, had just about every good Sierra adventure/quest game (including the original KQ).
Ah, memories.
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My first true all-PnC was Space Quest IV.