100 years ago racists wanted to prove that white men have better brains than everybody else. So they measured the skulls of women, Africans, and Jews and voilà! They had "scientific" proof that everyone they hate has bad brains. 

Over the last 20 years we've done exactly the same thing with teens and under 25s. We use cherry-picked junk science to "prove" that they are mentally deficient then we treat them like shit.