Sufficient to follow old model (7)
I believe the answer is:
example
'model' is the definition.
(I know that model can be written as example)
'sufficient to follow old' is the wordplay.
'sufficient' becomes 'ample' (both can mean enough).
'to follow' is a charade indicator (letters next to each other) (some letters go after or follow others).
'old' becomes 'ex' (prefix meaning former or onetime).
'ample' put after 'ex' is 'EXAMPLE'.
(Other definitions for example that I've seen before include "Something illustrating a general rule" , "Illustrative exercise" , "Case in point" , "Paradigm or model" , "Characteristic item" .)