Although his birth year is unknown, his name Umako suggests the possibility that he was born in the year of the horse, and based on the official record left in "Kugyo Bunin" (Ancient Office Records), which records his service as a government officer as being 55 years, some people estimate that he was born around 550, which was the year of Kanoe uma (metal-horse year).
生年は不詳であるが、名前の「馬子」は午年生まれであることに因む可能性もあり、『公卿補任』に「在官五十五年」とあることから、550年の庚午年前後であろうと推定する人もいる。