crumbly, n. — Green’s Dictionary of Slang

crumbly n.

also crumblie

[such people are fig. ‘crumbling away’]

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

1982		Barr & York Sloane Ranger Hbk 158: crumbly n. Sloanes aged 50–70, beyond wrinkly.
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.’.