ateliosis
ateleiosis
underdevelopment
underdevelopedness
immatureness
subnormality
underspecificity
mother wit
precociousness
precocity
debilism
adolescence
oligophrenia
underadditivity
youth
juvenile
infantilism
juvenile person
developmental age
oversensitiveness
infantility
underestimation
infantileness
undergeneration
wunderkind
underclassness
underpreparedness
not the sharpest tool in the box
baby
not the sharpest knife in the drawer
disability
not the sharpest tool in the shed
oversophistication
room-temperature IQ
subestimation
microgenesis
fledgling
caveman stage
big baby
chuunibyou
noetic
underqualification
maturability
mental age
dysrationalia
juvenescence
oldness
transyouth
juvenilism
inarticulation