From the Kamino fight in a Boku no Hero Academia fic in which All For One's real/original name is Mugen:
Quote:“So, you and your vaunted successor require little girls to fight your battles for you, All Might?” All for One taunted.
Smiling, All Might said, “Well, we needed someone with the same maturity as your apprentice, Mugen.” All Might was thrilled when All for One flinched at that. “But there would be ethical problems associated with hiring preschoolers.”