Mario Bros. At the age of 3. I still remember getting a mild electric shock when I attempted to plug in the FamiCom on my own for the very first time. Everything went downhill from there. Game consoles, Handheld game devices, PC games, you name it I've probably played it at least once.
I played the Cat game in 1986 I think..then came tetris and soon after I discovered Role playing typing games such as Space Quest and Leisure Suit Larry games.... I was 7 years old and didn't speak a word of English, used the dictionary to type sentences like "open door" or "talk to girl"
I'm not sure about the very first but I remember Street Fighter II on the Atari ST when I was a little kid. It came on about eight floppy disks and you had to do at least two disk changes for every single fight!
Contra was my very first game I played, ever. I used to play the game with my friend when we were in high school.