I'm always reading something, usually multiple books at a time.
So, I've been reading and/or listening to a whole lot of YA dystopian novels lately (maybe too many!), so I'm finding myself mentally cataloging various tropes I keep finding. One that keeps tweaking my "implausible" switch is the idea of preteens and teens being formally classified as adults and going through some official process whereby they choose their entire adult path. For example, in The Giver, there is the Ceremony of Twelve, where all the children observing that birthday (everyone observes birthdays on the same day in December) learn what career path the Council of Elders has chosen for them. In The Knife of Never Letting Go, Todd Hewitt is poised to officially "become a man" when he hits age 13 in the bizarro never-explained 13-month year system of New World. In Divergent, it is the 16-year-olds who take aptitude tests and then choose their virtue-based faction in which to take initiation.
I have posited elsewhere that this trope makes a certain psychological sense for YA readers, as they must feel that all of the aptitude testing and college choosing they are going through are forcing them to decide on their entire adult path (only later to find out how many times people tend to switch paths in life). I also realize that there are certain traditions going back into antiquity that mark a young age as official "adult," such as the bar and bat mitzvah. But such traditions are now considered entirely symbolic, and if anything, adulthood has become delayed. An undergraduate degree occupies the position that finishing high school once did. I think Kurt Vonnegut was prescient when, in Player Piano, he created a futuristic society where it was necessary to have a Ph.D. to pursue any kind of job track at all, including the type that never used to require any college. One needed, for example, a doctorate to become a cab driver. Traditionally, authors of dystopian novels have striven to create a society that could plausibly develop based on current, real-life conditions. They often serve as a jeremiad. "Look, if we continue this set of practices, here is where we could end up." Think 1984 and Brave New World.
So here is what I think would make more sense. Do a YA dystopian in which official adulthood happens when you complete an advanced degree. "You're a medical doctor and an adult! Congratulations, you are now ready to move out of mom and dad's house and get your own place!"