Temporal processing declines with age may reduce the processing of concurrent vowels. For this study, listeners categorized vowel pairs varying in temporal asynchrony as one sound, two overlapping sounds, or two sounds separated by a gap. Two boundaries separating the three response categories, multiplicity and gap-identification, were measured. Compared to young and middle-aged listeners, older listeners required longer temporal offsets for multiplicity. Middle-aged and older listeners also required longer offsets for gap-identification. For older listeners, correlations with various temporal processing tasks indicated that vowel temporal-order thresholds were related to multiplicity, while age and non-speech gap-detection thresholds were related to gap-identification.