Super Mario Bros. on the NES, and I was four if my memory serves me correctly. I didn't like it at first because I'd play with my older sister as Luigi, and she would pause it when I was over holes. I liked the Duck Hunt more that came on the cartridge with it. Then one day when she wasn't around I went to my dad's room and played it alone and found out when I wasn't being harassed by my sister with the pause button, I was actually really good. The rest is history. The first game I beat was Super Mario Bros. 3, and I was probably five or six... I wanna say six.