Savings teens waste; by middle-age gone primarily (4,3)
I believe the answer is:
nest egg
'savings' is the definition.
(synonyms)
'teens waste by middle-age gone primarily' is the wordplay.
'waste' indicates an anagram (I've seen 'wasted' mean this).
'by' says to put letters next to each other.
'middle' means to look at the middle letters.
'primarily' suggests taking the first letters.
The middle of 'age' is 'g'.
The first letter of 'gone' is 'g'.
'teens' is an anagram of 'neste'.
'neste'+'g'+'g'='NEST-EGG'
(Other definitions for nest egg that I've seen before include "Fund put by as a reserve" , "Money kept in reserve" , "Is it to encourage laying" , "Money saved for a rainy day - by bird?" , "reserves" .)