All of us have to go through being a teen but there are some people who have an irrational and persistent fear of youth and teenagers called ephebiphobia and most of them fear that teenagers are non-compliant and have rude behavior.
Most people have personally had a bad experience with a teenager that has made him conclude that a teen can be domineering, manipulative, authoritative and strong. Most teens are considered to be difficult, impulsive, and would insist on doing what they want to do and this can be a nightmare for parents.
Teens are also more concerned with their peers than the other people around them. They want to fit in, go with the gang resulting sometimes in defying rules at home and rules set by the parents, or sometimes hurting other people their age just to fit into a crowd and this causes fear especially in parents. In some societies, gangs involved in robbery and violence start in their teenage years and some get scared when they come across these gangs.
An ephebiphobe may develop symptoms of anxiety when faced with a teen. They may feel threatened and will do anything to avoid interacting with them.
Treatment includes psychotherapy, specifically behavioural therapy so they can be taught not to react with anxiety when they deal with teens. Medications are rarely needed.