I often think of that question as when did I use a computer for programming. The answer to that is using a Wang PC doing stuff in GW-BASIC because that was what it provided. If you abstract from the PC part I actually started earlier than that. Can anyone remember the Texas Instruments TI-58? I had one of those in the 6th grade of VWO in 1977. I remember being quite adept at programming the thing. So much that I even programmed the thing during exams to quickly do repeated calculations for me.
From there on I was always interested in programmable calculators remembering a similar one made by HP and slowly drifting towards computing. I can remember using a Commodore-64 and finally bought a ‘real’ personal computer – a two diskette machine with a CGA display that could be used to write documents in classical Greek. From then on it went down-hill 🙂