Senior man, fellow to entertain you in old-fashioned way (5)
I believe the answer is:
doyen
'senior man' is the definition.
(I've seen this before)
'fellow to entertain you in old-fashioned way' is the wordplay.
'fellow' becomes 'don' (both can mean an academic).
'to entertain' is an insertion indicator.
'you in old-fashioned way' becomes 'ye' (I can't justify this - if you can you should believe this answer much more).
'don' placed around 'ye' is 'DOYEN'.
Can you help me to learn more?
(Other definitions for doyen that I've seen before include "Group's senior member" , "Respected field leader" , "Senior member of a professional group" , "respected figure" , "Man who is the senior in his profession" .)