You old guys in Arab republic! (5)
I believe the answer is:
yemen
'arab republic' is the definition.
(I've seen this in another clue)
'you old guys' is the wordplay.
'you old' becomes 'ye' (historical version of 'you').
'guys' becomes 'men' (guy can mean a man).
'ye'+'men'='YEMEN'
'in' is the link.
(Other definitions for yemen that I've seen before include "Country to south of Saudi Arabia" , "nation" , "Country bordering Oman" , "Middle East country" , "Arab state" .)