At the End of the Apocalypse, the Male Protagonist Is Too Middle-Aged

At some point, the world was attacked by a sudden virus and almost completely destroyed. In the apocalypse, animals and plants attacked by viruses mutate, and only a few humans survive. They live in underground cities like livestock. When a crisis comes, mankind has to take action, and the battle to end the apocalypse begins. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.