My earliest computer memory is from second or third grade (1975-76). A guy brought a line printer with a modem coupling into our schoool. The program in question allowed you to enter a number up to fourteen digits (or something like that) and it would type out the written form of that number. I think half the class asked for 99,999,999,999,999. No, I don't remember what the written form is. It was a cool demo for as young as we were.
But my first memory of actually playing with a computer is of Adventure.
When I was about nine, I think, Dad took my brother, Greg, and I to his office. To keep us out of everyone's hair he handed us off to "the computer guy." Computer Guy sat us down at a terminal built into the side of a computer which spanned the length of the wall. I think I remember it having Digital's name on it and being mostly blue. It might have been a PDP-10 or -11, but I was too young to know one way or another, and the memories are old enough now that I can't even be sure about the color. Computer Guy started up Adventure and showed us a few basic commands to navigate and then left us alone to explore. At some point he came back and showed us the magic words xyzzy and plugh. Greg and I were completely hooked.
When I was twelve I got my first computer, an Atari 800. I chose it over an Apple II because I liked it's editing mode better and I thought I was going to program games. It was on my Atari that I first played Zork I. I think I played it for a month before I remembered playing Adventure at Dad's work. I became an Infocom junkie. I bought Zork II and III and Hitch Hiker's Guide to the Galaxy with my allowance. I bought InvisiClues.
In high school I got rid of my Atari and bought an Apple IIc. The computers at school were Apple's and I'd long since given up on programming video games. I wrote several different character generators for DnD in BASIC. Later on I tried to write one in Pascal, but the data structure I created to hold the characters was too big to compile. Some years later I sold my Apple IIc, the Okidata printer my Dad got me as a birthday present, and all my software to help pay for one semester of college.
In my first job after college, a coworker asked me why I always used the metasyntactic variables plugh and xyzzy. I recounted the tale of Dad's work and Computer Guy and Zork. After that conversation I got on the net and found a port of Infocom games to MacOS. I was so excited to get back in the little white house with the trophy case.
Five or more years later, I recounted the tale to another coworker. After hearing me reminisce about it for a while he said, "you'll like this, then" and promptly beamed me a copy of Frobnitz for my Palm III!