Temporal processing abilities generally decline with age. These temporal processing declines may reduce the ability of older listeners to use temporal cues for spoken language processing, such as for segregating multiple talkers. A concurrent vowel paradigm was used to examine categorization judgments for young, middle-aged, and older listeners based on temporal onset differences. Listeners categorized vowel pairs varying in temporal asynchrony as one sound, two overlapping sounds, or two sounds separated by a gap. The two boundaries separating the three response categories were determined for each listener, corresponding to multiplicity and gap-identification. Compared to young and middle-aged listeners, older listeners required longer temporal offsets for multiplicity judgment. Middle-aged and older listeners also required longer offsets than young listeners for gap-identification. For older listeners, correlations with temporal processing tasks indicated that temporal-order thresholds for vowels were related to the multiplicity boundary, while age and non speech gap-detection thresholds were related to the gap-identification boundary.