Auditory temporal processing likely contributes to the difficulty of older adults in understanding speech in noise. Gap detection is one measure of auditory temporal processing. In the present study, we relate this psychoacoustic measure directly to the perception of stop consonant type gaps in speech markers. Ability to detect gaps in speech and nonspeech stimuli was measured in young and old adults with good audiograms and also in young adults in conditions of simulated auditory aging. Auditory aging was simulated using temporal jittering to disrupt the periodicity of the signal. The markers surrounding the gap varied in duration (40 vs 250 msec) and in spectral symmetry. In spectrally symmetrical conditions, the leading and lagging markers were the same: the vowel [u] in speech conditions and a 500-Hz tone in non-speech conditions. In asymmetrical speech conditions, the lagging marker was the same as in the symmetrical conditions, but the leading marker was the consonant [s] in the speech conditions and a broadband noise (1 to 6 kHz) in the non-speech conditions. For the intact stimuli, the gap detection thresholds for both age groups in spectrally symmetrical markers were far smaller than in spectrally asymmetrical markers. In all conditions, gap thresholds were significantly smaller in young adults than in older adults. For both age groups, gaps between spectrally asymmetrical speech markers were detected better than gaps between analogous non-speech stimuli. It is argued that phonological knowledge compensates for auditory processing difficulties in both age groups. For the young adults tested under conditions of simulated auditory aging, gap detection thresholds in the symmetrical conditions were significantly larger than for either age group when intact stimuli were used; however, performance in the asymmetrical conditions was not worse. Both markers used in the symmetrical conditions were periodic (tones or vowels) whereas the leading markers in the asymmetrical conditions were aperiodic (consonants or noise bands); therefore, it is not surprising that the simulation of auditory aging has a pronounced effect on gap detection in the former but not in the latter conditions. The findings are discussed in terms of the different aspects of temporal processing involved in the detection of gaps in different types of stimuli and the age-related changes in different aspects of temporal processing as they may relate to speech perception. Research funded by the International Dyslexia Association, the Natural Sciences and Engineering Research Council of Canada and the Canadian Institutes of Health Research.