Green’s Dictionary of Slang

1. a fool, a tedious person.

1839–40		J. Cobb Green Hand I 84: You don’t suppose I’m such a gummy as to jump over here.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1930		‘Dean Stiff’ Milk and Honey Route 206: Gummy – a hanger-on. A bum who goes along with the crowd but never contributes.
1950		Goldin et al. DAUL 88/1: Gummy. A flunkey; a hanger-on, used to run errands and do menial tasks.

2. a toothless person or animal.

1908		Sun. Times (Perth) 29 Mar. 4/7: And, to judge by the way they [i.e. politicians] could bite, / They couldn’t be classed with the gummies.
1910		P.W. Joyce Eng. As We Speak It In Ireland (1979) 296: A gummy, a person whose mouth is all gums.
1926		Maines & Grant Wise-crack Dict. 8/2: Gummy – Man without teeth.
1933		(ref. to 1890–1910) L.G.D. Acland Early Canterbury Runs (1951) 380: Gummy – An old sheep that has lost its teeth.
2003		McGill Reed Dict. of N.Z. Sl. 94: gummy Toothless old sheep. ANZ late C19.