infantilism

Noun	1.	infantilism - an abnormal condition in which an older child or adult retains infantile characteristics
	2.	infantilism - infantile behavior in mature persons

amentia, arrested development, babyishness, backwardness, blithering idiocy, childishness, cretinism, half-wittedness, idiocy, idiotism, imbecility, immaturity, insanity, mental defectiveness, mental deficiency, mental handicap, mental retardation, mongolianism, mongolism, mongoloid idiocy, moronism, moronity, profound idiocy, puerilism, puerility, retardation, retardment, simple-wittedness, simplemindedness, simpleness, simplicity, subnormality