Is there such a thing as adolescent psychology?

There sure is! Some psychologists specialize in studying child and adolescent behavior. Some also specialize in treating children and adolescents who are struggling for one reason or another. .
Yes. There are psychologists that specialize in teens.
Yes. One of my specialties is working with teens and I teach a course in it as well. Teens have unique developmental challenges that adults and children don't face.
Yes. Child and adolescent psychology is a subfield of clinical psychology that is vibrant, alive, and well. In fact there is board certification in child and adolescent psychology by the American Board of Professional Psychology (ABPP).