In Octavian Nothing, coming of age isn't about overcoming some major obstacle midway through the book. The obstacle—slavery—is a birthright (if you can call something so terrible a birthright) from the beginning, and not just for the main character Octavian, but also for the American nation that's about to be born.
So coming of age has more to do with separation in this book: The protagonist has to learn to separate from the home and nation that supports his continued enslavement, while the colonies have to figure out what to do about colonial slavery as they try to become a nation free from British tyranny.
Questions About coming-of-Age
Does the nation come of age in the novel?
How is Octavian's development similar and different to the development of America?
What is the importance of Cassiopeia's death in Octavian's journey?
How do the perspectives of other characters impact Octavian's character development?
Chew on This
The only way for Octavian to grow up is to escape; the College only holds him back at a point.
Even though Octavian is ready to switch sides at the end of the novel, his coming-of-age process is identical to the way America develops into a nation.