Ancalagon
Dusty Dragon
I was 11 or 12 and it was Dungeoneer (from the Fighting Fantasy books).
Same! We were 12-13 and we used that system - aah, good old advanced fighting fantasy, I sometimes wish I could just fix the issues in that system and use that... ah well.
After a year or perhaps 2 of that, we switched to 2nd ed.
Looking back, some of my adventures were... pretty horrid :/