Green’s Dictionary of Slang

(UK society) an older person, aged 50–70 .

1982		Barr & York Sloane Ranger Hbk 158: crumbly n. Sloanes aged 50–70, beyond wrinkly.
1995		D.J. Enright Interplay 137: Another semiprecious stone from Coronation Street [...] ‘You can’t live in the past.’ ‘You can when you have no future.’ Note that the second speaker isn’t a crumblie or even a wrinklie: he just can’t find work.
1999		Indep. Rev. 19 Aug. 4: Ken Kesey, the beatnik crumblie.
2007		S. Westerfield Extras 37: ‘It was about this bunch of crumblies.’ Ren lay back across the couch. [...] ‘But stories about crumblies never go big.’.