Copying some BASIC programs from some magazine (PC World?) onto "QBASIC" in DOS on an IBM 286 in the early 90s. Or entering x86 ASM via debug.com in DOS from the computer manual (which contained a section on how to program using debug). I can't remember which was first.
Edit: It's interesting a lot of people seem to have a similar experience (thanks BASIC!). I thought there'd be more "I played with JS in the browser in early 2010", or "I attended a programming bootcamp after studying law to get an engineering job" type experiences as well.