For one, culture norms can change in less than a decade, much less 1964. In 1964 there was still legal segregation in the US. And whatever you think "natural" today might not be considered so in 2030 or 2040, much less 2019 + (2019-1964).
Second, it's not like the terms men and boys don't carry different attributes still today, or just because the anglosaxon culture is going through an Emo hyper-sensitive phase that everybody of the 8 billions in the world will have qualms to use the terms "men" and "boys" in such a matter (more capable, more mature, etc).
Second, it's not like the terms men and boys don't carry different attributes still today, or just because the anglosaxon culture is going through an Emo hyper-sensitive phase that everybody of the 8 billions in the world will have qualms to use the terms "men" and "boys" in such a matter (more capable, more mature, etc).