Specimen is old enough (7)
I believe the answer is:
example
'specimen' is the definition.
(I've seen this in another clue)
'old enough' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'enough' becomes 'ample' (ample means enough or plenty).
'ex'+'ample'='EXAMPLE'
'is' acts as a link.
(Other definitions for example that I've seen before include "Punishment" , "Characteristic item" , "warning" , "Illustrative case" , "Model - instance" .)