Not to stump you, but because I genuinely don’t know the answer and wonder if one of you does:
Who is the youngest person to win an Academy Award not in an acting category? Discount also the recipients of the Academy’s Juvenile Award, as they were all also actors.
At the moment, for youngest winner in a non-acting Oscar category, I suspect the answer is Markéta Irglová, who won the Best Original Song Academy Award four days before her 20th birthday.
Anyone else got a different answer? Let me know.