all:
retarded.
exceptionally smart, ahead of age in understanding:
unintelligent,
stupid.
noun:
expected,
slow,
postponed,
half-witted,
moronic,
cretinous,
later,
feebleminded,
tardy,
anticipated,
overdue.
n.:
belatedly,
middle,
tardily, Serotinous, altricious.