I started playing fully sometime around May or June of 2012 during release 1.2.5. I remember it being the current version for probably about two months, give or take, before I experienced my first update. That was at the very beginning of August, so I figure it to be May or June I started.
Before that (extending, at most, a month prior), I played the PC Gamer Demo, which was what made me want the game, and that was of beta 1.3 I believe. I much preferred the release 1.2.5 version after purchase.
I was first using a cracked client at first to see how the game was, then I fell in love with it. So a little later I bought the game, sometime around the 1.2.5 release (April 4, 2012). So, I've been going at it for around 2.5 years now!