@KittyMeowMeow,
You do sound like you are mature and smart for your age. I have two teenage daughters so I can see where you are coming from.
I think what you are missing is experience. Life experience. No matter how intelligent a person is - there is no replacement for experience. You could very well be much more intelligent than an adult, however, the adult will have much more life experience than you.
An adult has already been through going to school, graduating, getting and maintaining a job and career, raising children, maintaining personal finances, having relationships with a significant other, traveling worldwide, maintaining a home.
After years of experience (and being a pretty intelligent person myself) - I realize even at my age and level of intelligence, I realize I can learn something from almost anyone. People younger than me, people older than me -- so called less intelligent people -others have had different experiences than I have had and I can learn from them.
Do you think people maybe patronize you because you act or say things that may give them the impression you think you are smarter than them? Maybe you, without realizing it, are coming across as being arrogant? Maybe that is the reason they are doing it to you?
I remember a friend I had in high school - she was extremely intelligent - she had the most impressive vocabulary of anyone I knew. She would come across as arrogant and full of it - not saying you are- she was a sweetheart and once you got to know her - you knew she didn't mean it that way.
Maybe if you make yourself open to their life experiences, in turn, they will appreciate your maturity and intelligence.