The village kids all call him 'old man' affectionately.
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阿爹 is dialectal and old-fashioned — common in Wu (Shanghainese), Cantonese, and southern Mandarin areas, and in period dramas. In modern Mandarin people say 爸爸 (bàba) or 爹 (diē) on its own.
culture
The 阿- prefix is a southern affectionate pattern (阿哥, 阿姨, 阿公). Hearing 阿爹 in a film usually signals the setting is rural, historical, or southern Chinese.