Well I do remember using some in early schooling, I think as early as the age of 4 :S, that computer was some sort of DOS, I am not sure of details cant really remember that great back then....wow did not body start playing with computers like i did when i was young. Hack i am only 28
My first:
Operating system Commodore KERNAL/Commodore BASIC 2.0
http://upload.wikimedia.org/wikipedia/commons/9/9d/Commodore64.jpg
My first OS was a box when I was 3. (Best PC ever)
Joking a side my first OS was 95 and now vista... (I know would be better with the box... ) But to day I get 2 MAC computers YAY me = /