Green’s Dictionary of Slang

(US) a general term of address: friend, ‘old boy’; thus as nickname.

1928		Chicago Trib. 19 Feb. 34/1: I took a heavyweight bum [...] to fight [...] a battle schoolboy by the name of Young Studdy.
1932		Baltimore Sun (MD) 30 Oct. 9/6: ‘Studdy’ Looney decided to ‘organize’ the ashwagon drivers.
1946		Mezzrow & Wolfe Really the Blues 219: This hemp that you’re pushin’ is groovy studdy.
2018		Post Crescent (Appleton, WI) 4 Feb. A10/1: Studdy loved to have fun and knew how to have a good time.