Artificial intelligence (AI) disclosure in advertising is increasingly common, yet prior research reports mixed findings, with evidence of both favorable and unfavorable consumer responses. Drawing on schema congruity theory, this research proposes that brand age represents an important but overlooked boundary condition of consumer responses to AI disclosure. Three experiments demonstrate that AI disclosure reduces consumers’ interest in clicking advertisements for old brands, whereas this negative effect does not emerge for young brands. Further analyses reveal that AI disclosure creates greater schema incongruity for old brands, undermining perceived brand authenticity and subsequently lowering perceived product quality, which in turn reduces ad-clicking interest. These findings contribute to the literature on AI disclosure, AI-generated advertising, brand age, and consumer responses to AI-mediated marketing communications.