Green’s Dictionary of Slang

1. (orig. US) a very boring or old-fashioned person, esp. as applied by modern jazz fans to their antitheses, the fans of trad. New Orleans jazz.

1948		Collier’s 20 Mar. 88: The moldy figs [...] are certain that the greatest jazz ever played [...] was played in New Orleans in 1915.
c.1951		N. Algren ‘Watch Out for Daddy’ in Entrapment (2009) 152: I’d rather have his hate than some fat square-fig’s love.
1959		W. Balliett Sound of Surprise 211: The term ‘moldy fig,’ which is one of the aptest derogatory colloquialisms in the language, was first used in jazz to describe those who believe that the music has been in steady decline since around 1930.
1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 28: moldy fig – Put down word for a square person who always spoils all the fun because he doesn’t appreciate the finer things in life.
1993		R. Firestone Swing, Swing, Swing 330: The traditionalist critics, the so-called Moldy Figs, who championed recently rediscovered New Orleans old-timers like Bunk Johnson and George Lewis as the only true keepers of the flame.
2004		E. Wald Escaping the Delta 193: The New Orleans [jazz] purists were dubbed ‘moldy figs’ and eventually lost the battle.
2018		Twitter 24 Jan. 🌐 [hashtag for photo of ageing, white jazz band] #ReturnOfThe MoldyFigs.

2. attrib. use of sense 1.

1975

A. Goldman Lenny Bruce 23: Moldy fig Dixielanders blow above the bar to an audience of [...] out-of-towners.