A century old, but still in prison (5)
I believe the answer is:
caged
'in prison' is the definition.
(caged can mean imprisoned)
'a century old' is the wordplay.
'a century' becomes 'C' (common abbreviation).
'old' becomes 'aged' (similar in meaning).
'c'+'aged'='CAGED'
'but still' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for caged that I've seen before include "in prison" , "Cooped up" , "In a zoo?" , "Confined behind bars" , "Shut up" .)