Demonic Delight! Nezuko's Age Revealed: Is She Really Only 14? - Jhu Innovations
Webnezuko is 14 years old in the anime, but biologically 12 as a demon. She becomes human again in the infinity castle arc after taking a medicine from tamayo. Webi view it as since she's lived for 14 years she's 14 mentally, and 12 physically.
Webshe’s 12 when she turns into a demon and 14 when tanjiro goes to final selection (this is ignoring the fact that demons don’t age)
