(under 18 only please) Why do adults have such narrow stereotypical views on teens?

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Everything on the list. Just because their friend's daughter's BFF forever's (i dunno?) trasporter's daughter's (whatsoever) and the list goes on, fits into one of the stereotypes they automatically classify EVERY SINGLE TEEN THEY SEE as that!! It's so annoying and it's an insult. Not everyone is a Directioner or Belieber!! And look, teens DO work hard. Have they heard of Beth? She is like a million times more successful than the average adult. What is wrong with them.
(under 18 only please) Why do adults have such narrow stereotypical views on teens?
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