Many Marvel characters go back into the 30s too. The most popular ones are indeed "silver age" - Spider-Man, F4, X-Men, Avengers, etc, which is 60s so Marvel is safe there, but Marvel has a lot of characters from "golden age" from the 30s/early 40s - for example the original Captain America is 1941, Namor the Submariner is from the 30s, original Human Torch similarly.
But it's true most of modern Marvel IP is from 60s, and also it's hard to make an interpretations of the characters not based on the modern interpretations, and Marvel has trademarked everything from head to toes, including all the character designs and names (and even the term "super hero"), so... yeah who knows
But it's true most of modern Marvel IP is from 60s, and also it's hard to make an interpretations of the characters not based on the modern interpretations, and Marvel has trademarked everything from head to toes, including all the character designs and names (and even the term "super hero"), so... yeah who knows