Source: Adventures of Superman (1952-1957)
I can't claim to have watched a lot of George Reeves Superman, but what I've seen of its Jimmy seemed competent, if rather "gee whiz" comic booky. Which is fine. Born in 1928, Larson would have been 24 when he got the role, and 29 by the time it ended. He has sometimes claimed he was born in 1933, shaving 5 years off, so perhaps he knew he could play younger than he was and didn't want directors skipping over his C.V.