YA tropes focus on the hardships that teens go through growing up: sexuality, poverty, mental illness, racism, etc. and generally grasps the YA audience by giving them a story to be able to compare their teenage life experiences to.
Although Young Adult tropes focus on a certain age range, adults older than 21 also enjoy reading this genre as sometimes the books feature content more R rated, but still contain morals for the Younger Adult.
Examples of Young Adult tropes:
As we look through the list of books that I found for YA tropes, you can see a trend of bright colors, young characters, and a genre that would appeal to a younger audience; love stories, tragedies, trilogies, and an overall "teen vibe".