Why do adults convince themselves all teenagers are stupid?

So here`s my question. I`m turning 16 in about 4 months. I`m moving out in 2 years or so, done high school in 2 years, and my dream is to live in montreal and write. I am a poet. All my life for as long as I can remember I have loved reading and writing poetry. It`s wonderful to just get wrapped up in. I`m an intelligent person. Not mathematically, but I have an 89 in english and 95 in drama, I`m a strong reader, and I am very intellectual and literate. At school, and around other teenagers, I have to dumb myself down, sound stupid, because If I don`t, I`ll get my *** kicked for being `y` or `gay` . This aggravates me to no end, as I hate talking like an idiot and saying `yo`and `dude`and `sup`and `sick`and all the various teenage vernacular, but I have to. Now I was discussing my dream with my parents, of moving to montreal to write. And they both said that they were dissapointed I was aming so low. A shock off the bat but ok. What angered me was they both told me, im too young to be able to make art because i`m too stupid and simple. They said I cannot possibly write poetry because all I have to write about is hair and internet because I`m too simple and inexperienced as a teen to contribute anything of societal value. They said, our not even 16 yet, as if when i wake up in a few months time, 16, I`ll suddenly be able to make good art. This shocked and blew me off my feet that my own parents could be so narrow minded, ageist and arrogant. Why is it that adults think they`re so much better then teenagers? I mean sure, A LOT of us are stupid, harmful, violent and mischievous, but then again, just because some black people are gangsters does that mean they all are? Some mexicans sell drugs do they all? some gay people are hyper ual, are they all? some asians are bad drivers are they all? some teenagers are stupid little sods, are they all? My question which I hope you can answer is so: HOW can adults, who claim to be the wisest, most all knowing generation of people at the moment, be so blind and stupid as to think that just because I am a teenager I cannot make art? I cannot write good poetry? Do i not see the same tree`s, and pastures and streams as the adult? Do i not feel the same hurt, and pain, and love, and anger as an adult? Do I not witness the same war, and hate and violence and genocide as an adult? Because I am 15, am I not a person?