Flash Comics #1, dated January 1940 but first published in late 1939, had among its backup strips the first adventure of "Johnny Thunderbolt". A normal guy who spent the next eight years having entertaining mishaps caused by his magical powers, activated whenever he accidentally says the magic words "say you". He's fondly remembered and often still referenced today. And his first story is very specific about his date of birth - 7am on the 7th of July, 1917. He's 100 years old today!
Well, probably - four pages later, the narrator tells us the story is set "in 1939, when Johnny is 23", because it wasn't the kind of comic that makes a big fuss over little details like that, but I think it's still worth celebrating!