Acoustic amplitude modulation (AM) patterns carry important information, particularly in speech. AM masking, influenced by frequency selectivity in the modulation domain, is considered a crucial factor for speech intelligibility in noisy environments. Based on recent evidence suggesting an age-related decline in AM frequency selectivity, this study investigated whether increased AM masking in older listeners is associated with reduced speech intelligibility. Speech reception thresholds (SRTs) were measured using tone-vocoded speech and maskers with no modulation, broadband AM, or narrowband AM at varying modulation frequencies. AM masked thresholds were assessed for a 4-Hz target modulation frequency. The study included young (N = 14, 19-25 years) and older (N = 14, 57-79 years) listeners with normal hearing. It was hypothesized that SRTs would be higher for the older group with modulated maskers and that the age-related increase in SRT would depend on the masker's modulation frequency content. The speech intelligibility results showed that maskers with broadband AM produced higher SRTs than unmodulated maskers. However, SRTs varied little with masker-modulation center frequency across the range tested (2-32 Hz). While older listeners exhibited lower AM frequency selectivity than young listeners, they did not consistently exhibit higher SRTs than their young counterparts across maskers. However, there was a trend for the effect of age to be greater for maskers with broadband AM than for unmodulated maskers. Overall, despite supportive trends, the results do not conclusively demonstrate that older listeners are more susceptible than young listeners to AM masking of speech.