Same here, I couldn't put a number on the amount, especially before my twenties.
I hate fighting, but I will fight if I have no choice. I remember my first fight, I didn't fight back and went home to tell my dad that some boy had hit me at school, he replied "tomorrow you are going to go back and hit him, and you are going to win, if you don't I will beat you when you get home".
If I ever lost a fight as a child my father would beat me himself and send me back to carry it on, so I got into alot of fights, until I grew bigger, then mostly everyone was too afraid to fight me because I hit 5'9" by the age of 13 whilst they were all (boys included lol) still a whole lot shorter than me.
Wow, talk about tough love

Did he really want a son or something? It's one way of making sure you deal effectively with the situation if someone's harassing you, I suppose, but it does make me wonder if it's one of those cases where the cure is actually worse than the disease... Still, even this is better than the idiotic and oft repeated eadvice to ignore bullies to make them go away. No, they don't, it just encourages them to do something worse that you WILL react to.
I have studiously avoided getting into anything of the sort since I was a kid (and not too often then). When dealing with adults there is usually a way out before it gets to that stage, tempting though it is to punch the odd idiot sometimes (I will admit), and agressively though certain people like to posture. There is usually another way. Assertiveness rather than aggression is the key, especially if someone is liable to attack you. If you're neither backing down (and making an easier target of yourself in the process) nor giving them an excuse to get physical by being
too threatening yourself, it's pretty rare for someone to want to take that next step.
I have definitely headed off several difficult situations with people who were behaving in quite an out of control and dangerous manner recently by taking that approach. I do think my experience in working with the (dangerously) mentally ill in the past may have helped me in such situations (actually, one or two of them were while I was working with them, as I only stopped doing so recently).