Well, it’s not so hard to be a young looking grandmother if you are in fact young. Joan Bennett (1910-1990) was eighteen when she had her first child and all of 39 in the photo above. This LA Times article by Louis Berg cites a number of Hollywood stars who remained slim and young looking despite welcoming grandchildren: Marlene Dietrich, age 48 at the time of the article; Glenda Farrell, age 45; and Gloria Swanson, the oldest, at 49.
You might write this off as simple celebrity propaganda, where privileged women were used to convey almost impossible standards of beauty for ordinary American grandmothers. It is obviously that, but perhaps it is also part of the post-World War Two shift that brought us Mrs. Exeter—an older beauty advisor in Vogue. People were beginning to recognize that Americans—and especially American women—were living longer and staying active longer. “Grandma (new style) isn’t so good at knitting,” writes Berg. “Her hooked rugs would win no prizes; she would rather cut than hook a rug. Chances are she can’t make those wonderful molasses cookies–but she’s not so bad at cheesecake.” While his comments focus on Hollywood glamour, they do indicate that older women had a life beyond the home.
Just for the record—I never wear shorts. But then, I’m not a grandma yet.