youth is wasted on the young
you can't put an old head on young shoulders
disservice
nature-deficit disorder
hebephobia
puppyhood
nonuse
misopaedia
generation gap
loathfulness
the cobbler always wears the worst shoes
juvenile
oldness
unyouthfulness
poor-spiritedness
inadaptation
déclassé
let go
youthlessness
maleducative
immature
mismatchedness
boyish
throw back
socionegative
disability
lilliputianism
nonquality
misopedic
ungentility
childishness
nondependence
inarticulation
juvenoia
juvenility
bookish
undereducate
uneducate
unaccustomedness
unsatisfy
negatively privileged
impressionable
rob the cradle
problem child
limitation
unfulfillment
shabby-genteel
identity crisis
ineffectivity
time
doting
take down a notch
desensitize
low-class
numskull
outskilled
school refusal
unsuitability
disesteem
go off the boil
unchildishness
immaturity
misappreciative
fester
dynamic efficiency
weigh against
flotsam and jetsam
low-quality
innocence
demotivated
doggishness
stupidity
go over like a lead balloon
disadvantageousness
dissatisfiedness
tough titty
underawe
nondevelopment
qualitiless
tough cookies
unadjustment
grow up
unappreciation
neglected
maladaptive
nonimprovement
tough toodles
unimprovement
dissatisfyingness
incompatibleness
maladjustment
misocainea
inferiorness
leave someone cold
disassortativity
shrimpiness
disbloomed
tough tuchus