An even more amazing story, Marine Corps PFC Jack Lucas. Lied about his age and entered the Corps in 1942, at the age of 14. Had a military school background and a muscular physique, so the recruiters believed he was actually 17.
Lucas eventually wound up in a support unit in Hawaii. Determined to see combat, he stowed away on a transport headed for Iwo Jima. While the ship was at sea, he presented himself to the senior Marine officer onboard, who allowed him to stay (his previous unit had already listed him as a deserter). On Iwo, Lucas was advancing with two other Marines through a ravine when Japanese hand grenades landed near their position. Lucas used his body to cover two grenades, which detonated. His buddies assumed he was dead and moved on; a second group of Marines found him barely alive and summoned corpsmen, who evacuated him to a hospital ship.
When the way was over, Lucas returned to school, as a high school sophomore.
Jack Lucas: https://en.wikipedia.org/wiki/Jacklyn_H._Lucas
Addendum: As you might surmise, Jack Lucas was the youngest MOH recipient during World War II.