I've listened to the radio show, where he started very young, and grew up. I know from a few golden age comics that he mostly only appeared occasionally back then (including being retconned in for nameless copy-boy characters some too, it seems), and was still a kid. I understand it to be the television show to have really catapulted him in the comics. I know by Superman 86 (Jan, 1954) in the story "Jimmy Olsen, Editor" he looks more like I'm used to him looking and is being editor as part of boy's day, so wouldn't be grown. But when did he grow up, and become an adult character instead of a boy?