I've been in fights frequently while a kid, but that's way too long ago to remember. I never got involved in any fights during my teens, the only thing close to it was a guy getting into an argument with me at a party when I was 18. I was supposedly flirting with his girlfriend (in truth, she was just an old friend i hadn't seen for a while and we were catching up). He surrounded me with half a dozen buddies and tried to headbut me. Unfortunately for him, he only succeeded in knocking himself down. I still stood without a scratch and didn't really felt hurt. By this time my own friends had caught up with me and with the balance of power no longer tipped in their favor, they ran off with their tails between their legs.
Later four of them singled out the shortest, weakest looking member of our group and ganged up on him when he went home. As a phenomenally skilled martial artist, he kicked their asses
In my adult life, i've never had any trouble. Being 6'9" with a muscular build (used to be skinny) and tattooed upper body does probably help.