The word Ephebiphobia or the fear of youth is attributed to a 1994 article by Kirk Astroth published in Phi Delta Kappan. In the UK, this reverse ageism is also called paedophobia. The fear of young people has been a fixture of most societies. Youth are seen as brazen, adventurous and decadent. They are unmanageable and impossible to control. Their defiance of authority turns them into a threat.
I couldn’t find this word used in any book on Goodreads but I found it in an essay:
“Sure, Grossberg says, all generations worry about the generations that come after them. But such media hyperboles, Grossberg says, reflect such a spike in ephebiphobia — the fear of teenagers — that Rolling Stone described today’s adolescents as the “most damaged and disturbed generation the country has ever produced.”-Cherry Crayton, Are We Down on Our Kids?