Typical adult too old to go topless (7)
I believe the answer is:
average
'typical' is the definition.
(thesaurus)
'adult too old to go topless' is the wordplay.
'adult' becomes 'a'.
'too old' becomes 'overage' (I've seen this before).
'to go topless' means to remove the first letter.
'overage' with its first letter taken off is 'verage'.
'a'+'verage'='AVERAGE'
(Other definitions for average that I've seen before include "representative figure?" , "Normal amount" , "Mean, median or middling" , "The statistical norm" , "Normal; mean" .)