Why do your parents assume stuff about their own child?

they are preventing things and are warning you about it so if you do do it you already now the consequences so they think by telling you this things they might keep you from doing it

First of all, for every action there is a consequence. If you know this, then you also realize that
you are responsible for controlling these consequences. No, you are not too young to
understand this at all. I was a single mother(grandmother now)and brought my daughter
up with the philosophy. She understood and helped her out with her perspective on a a lot of
subjects and situations. Second of all, be sure to outweigh the consequence for the action.
Are you ready to take them? If so, you might actually be matureing. As far as parents worrying,
that comes with love, not just being a parent. They want the best and more for you, so while
they have a closer connection right now, they want to do all they can. You can start showing
them that you understand this and how you are maturing by helping out and following the
golden rule that I just past on. Good Luck!

I have found that if parents assume you're doing something they're usually right and consequence you to try and prevent the behavior from continuing.

i think parents just worry sometimes.
if you fill them in on more of what your doing they'll lay off a bit.