I have three: when I saw "Mario Bros." for the first time, it was Christmas, and my brother and sister and I had gotten it from my Grandpa and Grandma. I was three, I think, and they let my sister, who was one, have the controller for a little while, just for fun. Of course, being one, she was very confused and kept looking at us like we were green. But I was getting hysterical because she wasn't beating the level and time was running out, and I thought something terrible would happen to her if she let time go out! So I ran screaming from the room. Yea, I was three!
Secondly was when I beat MB3 for the first time. My heart was beating wildly in my 10 year old heart, and I was making silly mistakes in front of a very scary looking Bowser. But when I finally beat him, I ran around the house in glee.
Thirdly, when I was 13, I finally beat my brother (Roy Koopa) on Mario Kart GP 150. I was so stunned (and he was, too!) that I beat him, but I screamed and ran around the house telling everyone I met that I had finally beaten my big brother in a Mario game!
Exit, stage right! ;)