1.3 for me. a schoolmate of mine showed it to me at his place, got it on my pc the day after that. Got hooked ever since even though i only had a 56k dial up connection back then and could only play with bots for like a year.
Good memories you brought me bro ;)
Started with Source back in around 2005 to 2008 then again at late 2009 to 2011, tho i only played zombies,surf,deathrun and minigames on community servers. Switched to csgo in early 2015 and been playing since