Afaik career of actress was considered to be dead by the time she was 40 or so for most. Younger are more sexy, basically. Male actors could play big roles later. It is not that older women did not existed in real life. They outnumbered old men in real life.

Plus, movies always operated in fashions. What was depicted was heavily limited by big studios policies and by mandated codes. These limited topics and the way things were shown.

Movies are not reality and never were. They don't depict real life now either.