The biggest opponent I've faced relative to my size at the time was a big drunk construction worker when I was 13. I was at the company party, and we were both drunk. I said something to him, and he tried to throw me in the "pit" that they drive big trucks over to work on them.
As he pushed me back toward it, I just relaxed and waited. When we were almost there, I jumped down into it and threw him over the top of me. He bounced off of the metal I-beam, then flopped down and landed hard on the concrete. That was about it.
In karate, I fought a dude that was about 6' 6" and 240-ish. He was a black belt in TKD, and kept coming in with some of the wildest kicks I've ever seen. I got really sick of arm-blocking them, so every time he'd come with one, I'd jump right into it and leg-block it. Later in the locker room, he showed me his leg, it was bruised top to bottom from my leg blocks!
As for real fights, other than that drunk, dudes have been pretty much my size, not much difference. But I tend to stay out of trouble most of the time.
You fought a full grown dude when you were 13? and you were drunk? and at a company party, so you were working by the time you were just 13?
Times must be hard where you come from.