In the US, copyright status is determined by when something was published, not how old it is. The two are not related. That's how we get stupid things like the University of California and the Mark Twain Foundation claiming a copyright on his autobiography, written circa 1909, until 2047 - 137 years after his death.[1]

[1] https://en.wikipedia.org/wiki/Autobiography_of_Mark_Twain#Ma...