Drunk behaved like old youth (6)
I believe the answer is:
wasted
'drunk' is the definition.
(I've seen this before)
'behaved like old youth' is the wordplay.
I cannot really see how this works, but
'like' could be 'as' and 'as' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wasted that I've seen before include "Squandered or withered" , "Not used to good advantage" , "Used up needlessly or weakened through illness" , "Squandered, dissipated" , "Drunk (as a missed opportunity?)" .)