While I had basic idea about version control for code before that, I had started using it seriously for work projects several years ago.
At the time Subversion started to get pushed out by newer distributed systems. We went with Mercurial over Git back then for friendlier behavior and safer defaults.
In the long run rising popularity of GitHub had crippled Mercurial’s chances for being common enough choice. I had gradually moved on to Git. Most of that I credit not even to GitHub, but convenience and power of SourceTree version control client.