Old-fashioned old man penning note (5)
I believe the answer is:
dated
'old-fashioned' is the definition.
(thesaurus)
'old man penning note' is the wordplay.
'old man' becomes 'dad' ('dad' can be a synonym of 'old man').
'penning' means one lot of letters goes inside another.
'note' becomes 'te' (**).
'dad' placed around 'te' is 'DATED'.
(Other definitions for dated that I've seen before include "Went out with - old hat" , "Old fashioned" , "Outmoded" , "not without romantic engagements" , "Walked out with" .)