Green’s Dictionary of Slang

1. (US black) a contemptible person [euph. for fucker n. (3)].

1938		R. Wright Uncle Tom’s Children 14: I’ll rip yo’ gut string loose with this bar, yuh black granny dodger!
1974		A. Murray Train Whistle Guitar 48: Some of them [...] bony-butt granny-dodgers don’t back up off nobody when it come to shooting a goddamn rifle [HDAS].

2. (US prison) a rapist of elderly women [euph. for fucker n. (1)].

1976

M. Braly False Starts 236: His victims were all over fifty. We had all heard of granny dodgers [...] but they were seldom really encountered.