Which of these fighters were closest to their prime when Marciano them?

Joe Louis was 137 years old

 

Best way to estimate this is to look how close these guys where to the point where they were washed up.
Take Charles, the youngest, for example. Only 32 would lead you to believe he was close to prime, but take a look at his record at 1955 and you realize he was shy one year of being utterly washed up when he faced Marciano. Certainly, 1954 Charles was much better than 1955 and later Charles but he was dangerously close to the end of his effectiveness as a top fighter. When you look at the years leading to 1954 you get the idea. He was losing already yo Walcott, Johnson, Layne and Valdes, already was on the slide, but Marciano was the tipping point.
So was Charles closer to his prime than Walcott? I'd say they were about equally diminished.
Moore is the one who had the most success after fighting Marciano but even he got royally owned by Patterson the next year, so again, it's fair to say he was already diminishing at 41 but still had enough toughness and skill to deal with B tier fighters.
Walcott had his best run and best performances in 1945-1948. A lot of people take the Charles KO and the following decision win to argue for Walcott hitting his prime, but that doesn't make sense. It's equating one good KO win and a controversial decision against a slipping Charles over a multitude of victories vs Joe Baksi, Joe Maxim, Jimmy Bivins, Elmer Ray, Lee Oma, Lee Q Murray, Curtis Sheppard and a damn near victory over Joe Louis, who we know was still a dangerous foe considering the rematch. He was 32-34 when he scored all these victories, still lightning quick with his feet. He was a 39 year old when he and Marciano squared off.

Not a single one of Rocky's best opponents were even close to their primes when he matched them, but the one who had slipped the least would probably be Archie Moore, followed by Walcott and then Charles.

 

lol @ Louis even being an option.

 

Moore or Walcott for mine. Walcott really produced a turn-back-the-clock performance which doesn’t necessarily answer the question, but is worth noting.

 

Maybe Walcott, Charles was younger but worn. All of them had prime fading in the rear view mirror though.

 

Charles, 2 years older than Marciano and won 10 of his last 12 fights, so he wasn't washed.

 

A well considered and explained post.Kudos.

 

Moore by a long mile