Old enough model (7)
I believe the answer is:
example
'model' is the definition.
('example' can be a synonym of 'model')
'old enough' is the wordplay.
'old' becomes 'ex'.
'enough' becomes 'ample' (I've seen this before).
'ex'+'ample'='EXAMPLE'
(Other definitions for example that I've seen before include "Illustrative exercise" , "Something to be imitated" , "Something illustrating a general rule" , "lesson" , "Fact that illustrates a general rule" .)