Old-fashioned father drinking endless cha (5)
I believe the answer is:
dated
'old-fashioned' is the definition.
(dated can mean old-fashioned)
'father drinking endless cha' is the wordplay.
'father' becomes 'dad' (informal term for father).
'drinking' is an insertion indicator (inserted letters are consumed or drunk).
'endless' means to remove the last letter.
'cha' becomes 'tea' (I've seen this in another clue).
'tea' with its last letter taken away is 'te'.
'dad' going around 'te' is 'DATED'.
(Other definitions for dated that I've seen before include "Went steady" , "Walked out with" , "Antiquated" , "Old fashioned" , "Pass" .)