Iron Munro, would be one of the DC Universe's earliest known metahumans appearing in Shadow Comics #1 in June 1940.
Iron Munro is the son of Hugo Danner who was also born with superhuman ability via a serum created by his father Abednego Danner in 1894. Hugo was born with superhuman strength, speed and invulnerability. But technically he was changed in the womb by his father's serum so he would not meet the grade, but his son Iron Munro would.
Munro was the child of Hugo Danner and a Colorado woman named Anna Blake. Munro was born with superhuman powers and possessed incredible strength and invulnerability by the age of ten.
This particular version of the character gained greater notoriety after the Crisis on Infinite Earth's when DC restructured their universe and erased the Earth-2 Superman replacing him with Iron Munro.
Iron Munro is a fictional superhero, who first appeared in Shadow Comics #1 (June 1940), published by Street & Smith. He is loosely based on Aarn Munro, the hero of a series of short stories written by John W. Campbell in the 1930s. The modern and better known version of the character, who started life as Arn Munro, first appeared in Young All-Stars #1 (June 1987) and was created by Roy Thomas, Dann Thomas, Michael Bair and Brian Murray. Munro is the illegitimate son of Hugo Danner, the superpowered protagonist from the 1930 novel Gladiator by Philip Wylie. However, Iron was not a character or even a possibility in the original novel. Hugo's inability to pass on his powers to his children is explained by his ailing scientist father, "the effect of the process is not inherited by the future generations." --Wikipedia entry: Iron Munro
As a side note: I reviewed all of DC's earliest properties particularly among the Mystery Men and almost all of them failed to meet the criteria due to their use of various technologies to give them their abilities. Those who were not technology users had their powers bestowed by accidents, divine forces, or medical/drug technologies.
- The Mighty Atom: No powers in his first incarnation
- The Flash: Received powers in a radiation accident
- The Sandman: Gas gun, gas mask, armored coat
- Hour-Man: Miraclo pill - super-strength, speed, stamina for one hour
- The Spectre: Revenant; granted superhuman magical abilities
- Green Lantern: Bearer of the Green magical energy and ring
- Wonder Woman: formed from clay and given life and power from the gods
- Doctor Fate: powers derived from wearing the helmet of Nabu
- Hawkman: magical wings and medieval weapons
- Doctor Mid-nite: Visually-impaired, used technology to augment vision
- Johnny Thunder: magical connection to Thunderbolt
- Starman: Cosmic rod used to control light energy