I purchased and started playing Terraria for the first time on September 13th, 2011. I remember that Hardmode wasn't added to the game yet back then.
I played with my cousin and some friends the first time I played it, I still have the world we played on. (but I never play on it anymore)
And I guess I'll also put my amount of hours played here (image from 29.09.2016)
I confess, I was once a pirate and so had an illegal copy of Terraria. Not anymore.
Well... I first downloaded Terraria illegally around May 2012 (version 1.1.2) and started playing it. I don't know how many hours clocked in there, since hey, I didn't keep track of time, also I didn't use Steam.
But in terms of legal Steam version...
A friend gifted it to me around October 2013, (version 126.96.36.199.1) and since then I've clocked over 650 hours in it.
Most of those hours were from 2013 and 2014 anyways. 1.3 added around a 100 hours to it. I lose and gain interest in it from time to time.