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