According to historical materials in which he is recorded as 'the former governor of Yamato Province, Jugoinojo (Junior Fifth Rank, Upper Grade), MINAMOTO no Asomi Mitsuyuki' it is discerned that he had already served as the governor of Yamato Province in his twenties.
史料には「前大和守従五位上源朝臣光行」と記載されていることから、二十歳代で大和守になっていたことがわかる。