Who is the youngest posthumous Medal of Honor recipient?

Private First Class Robert Charles Burke (born Nov. 7, 1949, in Monticello, Illinois) was a machine gunner in the 3rd Battalion, 27th Marines, 1st Marine Division, in Vietnam. While on Operation Allen Brook, his company came under intense fire. Burke seized his machine gun and launched a series of one-man assaults against the fortified emplacements in order to allow his units to advance and evacuate casualties. He fell mortally wounded at the age of 18.

He was the fourth youngest person to receive the Medal of Honor, the youngest to have fought in Vietnam and the youngest to receive it posthumously.

https://www.defense.gov/News/Feature-Stories/Story/Article/2599520/medal-of-honor-monday-marine-corps-pfc-robert-c-burke/

https://www.oldest.org/people/youngest-medal-of-honor-recipient/