We're Alone in This World (fem oc x sapnap)

What if in an overpopulated, war torn world, US government officials settle on an experiment to "eliminate" every human aged below 12 or above 18 to create a fresh start to avoid war? And what if that said experiment went wrong, and instead of setting the population to rest, they created a species of zombie-like creatures? What if the remaining teens have to fight everything around them to survive, facing a crumbling society where becoming an adult means so much more than working a 9-5.