Sultan’s palace complex is large and old (8)
I believe the answer is:
seraglio
'sultan's palace' is the definition.
(I've seen this before)
'complex is large and old' is the wordplay.
'complex' is an anagram indicator.
'and' says to put letters next to each other.
'old' becomes 'o' (abbreviation).
'is'+'large'='islarge'
'islarge' with letters rearranged gives 'seragli'.
'seragli'+'o'='SERAGLIO'
(Other definitions for seraglio that I've seen before include "Harem - eg sailor (anag)" , "Harem - or silage (anag)" , "Muslim wives" , "Gaolers I mixed up in harem" , "Women's apartments in a Muslim palace" .)