Look over lair of a former age (5)
I believe the answer is:
olden
'a former age' is the definition.
(I've seen this before)
'look over lair' is the wordplay.
'look' becomes 'lo'.
'over' says the letters should be written backwards.
'lair' becomes 'den' ('den' can be a synonym of 'lair').
'lo' backwards is 'ol'.
'ol'+'den'='OLDEN'
'of' acts as a link.
(Other definitions for olden that I've seen before include "(Of days) in the long distant past!" , "as in time gone by" , "times gone by" , "Of past (times)" , "Former, past" .)