Green’s Dictionary of Slang

an older man whose sexual tastes (whether or not fulfilled) err towards much younger lovers, esp. when under the legal age of consent.

1883		‘Three Chums’ in Boudoir vi 89: ‘You’re a darling young fellow, so different from the dirty old men we generally pick up here’ .
1920		J. Huneker Painted Veils [ebook] ‘Don’t tell me another thing about the dirty old man, or I’ll hate you’.
1934		J. O’Hara ‘Over the River and Through the Wood’ in New Yorker 15 Dec. 25/2: There was cold murder in the girl’s eyes, and loathing and contempt [...] ‘Get out of here, you dirty old man’.
1940		F. Sargeson ‘A Man and his Wife’ in A Man And His Wife (1944) 75: We all chipped in to say he was a dirty old man, and it was no wonder his missis had kicked him out.
1945		‘Michael Innes’ Weight of Evidence 116: Nor did Prisk appear to be a mere collector of anecdotes of Cyprian experience. Much of what he had to say took the form of personal reminiscence. In fact, thought Appleby, a thoroughly dirty old man [Simes:DLSS].
1957		J. Braine Room at the Top (1959) 133: ‘What’s a DOM?’ [...] ‘Dirty Old Man.’.
1959		K. Waterhouse Billy Liar (1962) 39: He’s got a mucky book under his jersey! Coarrr! Dirty old man!
1960		J. Iggulden Storms of Summer 34: Christ! You make me sound like a dirty old man, the way you say that.
1964		Lavender Lex. n.p.: dirty old man:-A slightly mocking term applied to someone older than the speaker. Sometimes applied to persons in the twenty’s [sic] but most often applied to those above 40. Has but little to do with being old and absolutely nothing to do with being dirty. Usually denotes someone who engages in sex with the younger generation as an insertor.
1967		N. Dunn Poor Cow 81: Here I am touching up this dirty old man for a couple of quid.
1970		‘Troy Conway’ Cunning Linguist (1973) 01: ‘That old lecher. Look at him. The prototype of a dirty old man.’‘An ass-pincher if ever I saw one,’ I agreed.
1984		Benjamin & Pearl Limericks Down Under 39: A dirty old man of Tarcutta / Was an unregenerate rutter.
1985		K. Vacha Quiet Fire 70: I don’t mean to be a lush or a dirty old man in a bar.
1998		D. Senna From Caucasia, With Love (2000) 66: There are perverts, crazies, dirty old men, and they want little girls like you.
1999		Guardian Guide 19-25 June 4: It also has the Dirty Old Man demographic by the short hairs.
2006		www.downloadingpornwithdavo.com 🌐 The Dirty Old Man. He’s a public pervert! And truly proud of it! Watch him fuck young women!