I think I was around 11 when I first played.
My parents got it (Civ 1 for Windows) when I was 6, but they wouldn't show me how to play or anything, they just said "It's really complicated". Eventually I started to resent the game because my parents would hog the only modern computer playing it, but over time (and after playing games like SimCity and Age of Empires instead of just Mario and Zelda) I became more and more interested in the game. I started reading books about Civ and asking my dad questions about it as I watched him play, and then I started a game of my own with him explaining what to do and why. Some things I picked up quickly, like which units are good to use for what and how to improve the terrain, but it took a longer time for me to understand technologies and governments...at first I just picked technology at random unless it was something I knew was good like Railroad or Automobile.
When I started playing without Dad's help, I didn't know to switch governments and just stayed in despotism the whole game. I think I almost conquered the world once, but I couldn't find the last few cities and eventually ran out of money. I didn't know how to keep people happy other than with lux, so I ran like 90% lux and would buy stuff a lot when I got into civil disorder, so I think I went from 3000 gold to like 100 gold in only a few turns. I knew there was a wonder that let you see all cities, but my research had to be set to 0 around Flight, so I could never get it.
The first time I won, it was in 2095 or something, right before the end of the game. I was so happy even though it was just Chieftain with 3 civs...