Don't you lock up something that you wanted to see fly

[Zephyr of Darkness]

Say.....though it's not what you're supposed to do, I agree with senjuro. You should do whatever you want in your life, if you can. There's plenty of things you'd want but you can't, so if you can.....Look, I have my dog's example. We were sure that, considering the way we took care of him, he was going to live at least 15 years, or maybe 20. That goes for everyone too. You never know how much you are going to live, so you have to do it to the fullest.
But in any case, before you start training warm up adequately. At least 15' (and 30 or 40, if you can). That should reduce your possibilities of spraining.

PS If all you want is venting your anger kicking, maybe you can start a safer activity.

Oh, and sth else:

Nah, as long as you practice clean technique, you should be perfectly healthy well into your later years.

That's not quite true. To tell you a simple example: Have you heard of the "marching fracture"? It's a fracture in the base of the 3rd metatarsal that marching soldiers used to have. They marched for days, and the constant beating ended up fracturing the bone. Now, will you say that they got fractured cuz they didn't know how to walk with a clean technique? I said a very obvious example here, but there are plenty.