Robert B. Ray, in his book How a Film Theory Got Lost and Other Mysteries in Cultural Studies, provides this 1868 quote from Théophile Gautier --
“Faced with this paradox in painting, one may give the impression – even if one does not admit the charge – of being frightened lest one be dismissed as a philistine, a bourgeois, a Joseph Prudhomme, a cretin with a fancy for miniatures and copies of paintings on porcelain, worse still, as an old fogey who sees some merit in David’s Rape of the Sabines. One clutches at oneself, so to speak, in terror, one runs one’s hand over one’s stomach or one’s skull, wondering if one has grown pot-bellied or bald, incapable of understanding the audacities of the young… One reminds oneself of the antipathy, the horror aroused some 30 years ago by the paintings of Delacroix, Decamps, Boulanger, Sheffer, Corot, and Rousseau, for so long excluded from the Salon… Those who are honest with themselves, when they consider these disturbing precedents, wonder whether it is ever possible to understand anything in art other than the works of the generation of which one is a contemporary, in other words the generation that came of age when one came of age oneself… It is conceivable that the pictures of Courbet, Manet, Monet, and others of their ilk conceal beauties that elude us, with our old romantic manes already shot with silver threads.”
Gautier's gut feeling was that Courbet, Manet, Monet etc. -- painters whose work at that time was too controversial to be admitted to the Salon -- were not “art.” But remembering how obdurate his elders had been, back when he himself was defending Delacroix, Gautier could ponder at an intellectual level whether part of the problem might not be some kind of age-related decline in neuroplasticity. Extending this line of thought further, Gautier might have considered that he was probably also biased against Jacques-Louis David...
I bring this up when guys in their forties tell me popular music stopped being good in the 1980s, or when guys in their fifties tell me popular music stopped being good in the 1970s. Usually what this gets me are disgruntled skeptical codgerly looks... Most people have some degree of bias towards the cultural output of their own generation: this is easiest to spot in people from generations other than our own. Nowadays someone walking through the Louvre from David to Delacroix to Degas to Dufy might perceive mostly continuities and not suspect how much generational conflict was going on...