Computer graphics people like to talk about the uncanny valley - the idea that making an animation character look sufficiently realistic can make people dislike the character - because suddenly they see it as a flawed human, rather than as a fictional character skillfully evoking a human. Thus the reaction quickly becomes negative, not positive.
I think the same effect occurs with actual humans - specifically teenagers.
There are basically three kinds of humans: adults, kids, and teenagers. Adults are useful to other adults - they "speak" a common psychological language, which makes it easy to communicate with them and easy to get things done together with them.
Kids, on the other hand, are pretty much useless to adults, but they are cute. The "cuteness" factor is not exclusive to kids - we also find many animals to be either cute or just entertaining. Apparently with both kids and animals, we recognize them as different from us, and accept them as fine examples of whatever they are, and thus end up liking them.
Teenagers have neither advantage. They are sufficiently different from us that they are rarely useful. But they are too similar for us to appreciate them as different. And thus we, the adults, simply find them annoying.