Out-of-date old boys look back, wanting summer in Paris (8)
I believe the answer is:
obsolete
'out-of-date' is the definition.
('obsolete' can be a synonym of 'out-of-date')
'old boys look back wanting summer in paris' is the wordplay.
'old boys' becomes 'obs' (I've seen this in other clues).
'look' becomes 'lo'.
'back' is a reversal indicator.
'wanting' says to put letters next to each other.
'summer in paris' becomes 'ete' (').
'lo' written backwards gives 'ol'.
'obs'+'ol'+'ete'='OBSOLETE'
(Other definitions for obsolete that I've seen before include "No longer produced or used" , "Old hat" , "Outdated" , "Pass" , "Outmoded, passe" .)