I'm 19 and my first introduction to the series was just because my family had KQ5 and KQ7 lying around. Both the fully voiced versions, and Cedric lends himself quite well to childhood nostalgia in my opinion.
I'm not quite sure why I took to it so much, but I did. I joined the Sierra forums for King's Quest at around...I want to say 9, and started giving my parents back my allowance money and begging to use their credit cards to get the rest of the KQ games off eBay. I bought KQIV, KQV, KQVI, and KQVII separately, and then the KQ collection 1-6 as well (I had a bad habit of scratching discs at that age). Since I later bought the KQ Compilation, I bought most of the series at least 3 times.
When I was in 4th grade, I learned that there was an 8th King's Quest game and convinced my mom to take me to the computer store to buy it. This was a few years after the game came out, so I'm sorta surprised I found it, but it was there. I picked up the box, looked it over, decided it had nothing to do with King's Quest and walked out empty-handed. I remember I was convinced that the game would star Valanice since she'd only had half a game to star in so far.
I know at some point I stumbled across the KQIX site, in all of its light blue glory. I downloaded some of the music tracks and tried to keep up with it for a while, but there were no updates, so I didn't really bother until some point when I was 11. It wasn't until one of the more prolific members of the Sierra forums said he was leaving for this KQIX thing that I felt compelled to look it up (Hi, CC!) I kept up with both forums for a while, but I found a home here.
All the same, that means I've been on these forums for almost 8 years. I feel compelled to apologize for all of the growing pains all of the other members have had to deal with me having.
But in short, the games were around; they were fantastic, and Google is your friend.
All that said, I honestly wouldn't be surprised if KQ, TSL and the forums kind of shaped the career path I'm on now. I know it's a bit off topic, but King's Quest is what got me into adventure gaming, which is what got me into fanmade adventure games, which is what got me into the idea that creating your own games is something that's a real possibility, and I've been pretty much trying to create a magnum opus (Or at least a really awesome portfolio piece) ever since.
Pretty much for most of my conscious life, King's Quest and I have been intertwined. There's a reason I go by Rosella pretty much everywhere on the internet.