noun

the state of being immature or not fully grown.

the immaturity of the immune system in very young children makes them especially vulnerable

unripeness,greenness,sourness,newness,rawness,crudeness,crudity,imperfection,incompleteness,lack of completion,lack of development,childishness,babyishness,infantilism,juvenility,puerility,lack of experience,inexperience,unworldliness,naivety,ingenuousness