Push out old boy over time getting ill-mannered (7)
I believe the answer is:
obtrude
'push out' is the definition.
('obtrude' can be a synonym of 'push out')
'old boy over time getting ill-mannered' is the wordplay.
'old boy' becomes 'ob'.
'over' says to put letters next to each other.
'time' becomes 't'.
'getting' says to put letters next to each other.
'ill-mannered' becomes 'rude' ('rude' can be a synonym of 'ill-mannered').
'ob'+'t'+'rude'='OBTRUDE'
(Other definitions for obtrude that I've seen before include "Barge in" , "Redoubt (anag) - become noticeable in an unwelcome way" , "Thrust oneself forward" , "Make unpleasantly noticeable" , "Stick out unpleasantly" .)