11 years ago. Martin a few years ago gave an interview where he stated that he uses a modern PC now, assembled by one of his assistants (and I assume modern software).
But the modern PC still uses DOS and WordStar lol.
"Well, he doesn’t actually write on an old DOS computer. He did write on an old DOS computer, and then it died. Actually, I built him the computer he writes on now, which is a state-of-the-art machine running DOS and WordStar 4.0."
- GRRM's employee
https://en.wikipedia.org/wiki/WordStar
https://www.sfwriter.com/wordstar.htm