easier in black & white
Actors (& every body else) also just looked older back then
These are both correct answers. I'm 54. I remember looking at my parents high school annuals and thinking everyone looked 35 years old.
People's health in general was worse and they didn't live as long as we do. Their bodies had reached that state in only 16-17 years.
Women have always wanted to look younger. Most men back then weren't as vain and had no desire to look younger than they really were until they were in their 40's.