I started at age 6 or 7 by trying to mimic the command lines printed by my parents' first PC XT's AUTOEXEC.BAT (which lacked "echo off", for which I am eternally grateful), then checking out adventure books from my elementary school library where part of the story required typing in and running BASIC code.

I was also given an Atari 130XE by an uncle that booted to BASIC, explored GORILLAS.BAS when DOS 5.0 came along, etc.