This study presents a listening evaluation of a consonant enhancement method for older adults with mild hearing loss. The method selectively enhances word-initial consonants (fricatives, plosives, affricates, nasals) using phoneme-specific high-frequency boosting, amplitude gain, and time stretching. Synthetic Japanese speech was tested under three conditions (unprocessed, conventional high-frequency enhancement, proposed). Twelve older adults (68–77 years; no hearing aids) transcribed words in controlled sessions, and pure-tone and speech audiometry were administered. The primary outcome was word recognition accuracy (% correct over 13 words), with secondary analyses by initial-phoneme category and correlations with audiometric measures. The proposed method improved intelligibility for voiceless plosives and nasals, while results for voiced plosives varied by individual. Recognition accuracy correlated more strongly with speech audiometry than with pure-tone thresholds. These findings highlight individual and phoneme-level variability and support consonant-specific, personalized processing to improve speech understanding in older adults.