old lag
/ˌəʊl(d) ˈlaɡ/slang
noun
1Chiefly Australian. A former convict, especially one who was transported or sentenced to penal servitude.
2A hardened or habitual prisoner; a recidivist. In extended use: = old hand.
Origin
Early 19th century; earliest use found in James Vaux (1782–c1841). From old + lag.