It’s not easy to find vintage photos of older women in swim wear. Like me, perhaps many were adverse to pictures with too much skin exposed. But this smiling woman shows no such compunction. It’s hard to guess her age–her hair looks to be going grey and her male companion is no spring chicken. However the child they are watching is young. Perhaps she was in her forties with her youngest child. Or maybe she was a very fit sixty with her grandchild.
The eBay photo isn’t dated, but the swim suit style comes from the forties, with it’s bra style top and high waist bottom. I found a similar look in the 1942 Sears Spring catalog, and it was still there four years later. Like this style? You can make your own from current sewing patterns, like the Sophie swimsuit from Closet Case Patterns.