To conclude the discussion on Nezuko Kamado's timeline and her eventual relationship with Zenitsu Agatsuma, it is essential to look at how the story wraps up in the manga's final chapters and modern-day epilogue.

When Nezuko initially transforms into a demon, she is biologically twelve years old. Because her physical aging process halts during her time as a demon, she remains at that developmental stage for a significant portion of the main narrative. However, following the conclusion of the final battle against Muzan Kibutsuji, Nezuko successfully regains her human form and resumes normal human maturation.

As the narrative transitions into the peaceful era depicted in the final chapters and the modern-day descendants' epilogue, the characters grow up off-screen. Zenitsu's long-standing affection for Nezuko eventually develops into a mutual bond after the conflicts end and they have time to mature. While the exact calendar year of their wedding is not explicitly stamped with a single numeric age in the text, contextual clues from the post-series timeline indicate that they married well into their late teens or young adulthood, after Nezuko had fully returned to human life and years had passed following the final battle.

Their descendants—such as Yoshiteru and Tokuko Agatsuma—appear in the modern-day era, cementing their legacy. This concludes the comprehensive look at Nezuko's age progression, her transition back to humanity, and how her relationship with Zenitsu ultimately blossomed long after the dust settled on the Demon Slayer Corps' battles.