Sorry to hear how you feel. It seems like you're feeling quite hurt, and so you feel very angry.
I think it's important to realise that turning 18 is just a number. Yes, under the eye of the law, we are considered adults, but that's the only place where this is the case. We are still growing, and all at different stages of development. Turning 18 doesn't magically make us adults, it is a transition! Is there something in particular that you'd like to do but can't because of the age restriction?
The other thing I noticed is that you've said that you should have more power to tell people how you feel, and how you want things to change for you in a positive way. What would you do/change?
Much love <3