Purpose: In situations with a competing talker, lexical properties of words in both streams affect the recognition of words in the to-be-attended target stream. In this study, we tested whether these lexical properties also influence the type of errors made by listeners across the adult life span. Method: Errors from a corpus collected by Helfer and Jesse (2015) were categorized as phonologically similar to words in the target and/or masker streams. Younger, middle-aged, and older listeners had produced these errors when trying to identify key words from a target stream while ignoring a single-talker masker. Neighborhood density and lexical frequency of target words and masker words had been manipulated independently. Results: Lexical properties of target words influenced all types of errors. With higher frequency maskers, the probability of responding with a masker word increased and the phonological influence of target words decreased. Lower levels of lexical competition for maskers increased the probability that listeners reported a word phonologically related to both masker and target words. The influence of masker words increased across the adult life span, as evidenced by phonological intrusions into responses and the temporary failure in selectively attending to the target stream. The effects of lexical properties on error patterns, however, were consistent across age groups. Conclusions: The ease of recognition of words in both attended and unattended speech influences the breakdown of speech perception. These influences remain robust across the adult life span.