@ botodopo This is how it works: When a female ghoul gets pregnant for the first time, she stops physically aging.
Zadiris looking more youthful than the other ghouls simply means she got pregnant that early in her life. Then she went on living centuries+decades looking like that.
So if Basdia gets pregnant at the age of 25, she will look 25 for hundreds of years, unlike the other female ghouls, who look like teen moms.