Old Peruvian in prison (5)
I believe the answer is:
incan
'old peruvian' is the definition.
(I've seen this before)
'in prison' is the wordplay.
'prison' becomes 'can' (the can is American slang for prison).
'in'+'can'='INCAN'
(Other definitions for incan that I've seen before include "Like some South Americans" , "like former S American civilisation" , "Of ancient Peruvians" , "Of a native Peruvian" , "From old Peru" .)