The good fellow is evidently not young (4,5)
I believe the answer is:
grey friar
'evidently not young' is the definition.
The definition suggests a singular noun which matches the answer.
'the good fellow' is the wordplay.
I cannot quite understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is found within the answer.
'fellow' could be 'f' (abbreviation - of a society etc.) and 'f' is present in the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Another definition for grey friar that I've seen is " Franciscan".)