<p>Age similarity between communicators is often assumed to enhance persuasive effectiveness; however, empirical findings remain mixed, particularly in voice-based contexts. The present study examined whether nonlinear interactions between speaker age and listener age shape how listeners’ perceived emotions and voice impressions mediate purchase intention in advertising speech. On the basis of the Stimulus–Organism–Response framework, we conducted a large-scale online experiment in which participants across a wide age range evaluated synthesized advertising speech produced by 26 speakers spanning a broad age range. Participants rated perceived emotions, voice impressions, and purchase intention. Polynomial moderated mediation analysis revealed significant nonlinear speaker–listener age interactions. Significant three-way interaction effects were observed in stimulus-to-organism pathways involving speech features and the organism-to-response pathway for pleasure. These findings suggest that age effects on purchase intention are not fully captured by a simple age-matching account. Rather, nonlinear interactions between speaker and listener age modulate emotional and perceptual mediation processes underlying persuasive outcomes in advertising speech.</p>