Purpose: As children mature, changes in voice spectral characteristics co-vary with changes in speech, language, and behavior. In this study, spectral characteristics were manipulated to alter the perceived ages of talkers' voices while leaving critical acoustic-prosodic correlates intact, to determine whether perceived age differences were associated with differences in judgments of prosodic, segmental, and talker attributes. Method: Speech was modified by lowering formants and fundamental frequency, for 5-year-old children's utterances, or raising them, for adult caregivers' utterances. Next, participants differing in awareness of the manipulation (Experiment 1A) or amount of speech-language training (Experiment 1B) made judgments of prosodic, segmental, and talker attributes. Experiment 2 investigated the effects of spectral modification on intelligibility. Finally, in Experiment 3, trained analysts used formal prosody coding to assess prosodic characteristics of spectrally modified and unmodified speech. Results: Differences in perceived age were associated with differences in ratings of speech rate, fluency, intelligibility, likeability, anxiety, cognitive impairment, and speech-language disorder/delay; effects of training and awareness of the manipulation on ratings were limited. There were no significant effects of the manipulation on intelligibility or formally coded prosody judgments. Conclusion: Age-related voice characteristics can greatly affect judgments of speech and talker characteristics, raising cautionary notes for developmental research and clinical work.