I don't see why, if it is an environment where younger women are sunbathing topless, older women should not do the same, if they enjoy the feeling. Judging their breasts as not fit for human view is, surely, buying into the idea that breasts exist for decoration and the entertainment of men.
Breasts come in all shapes and sizes from almost non-existent bumps to big billowing ones but the media keep presenting this image of 34-38 D cup and probably silicone "enhanced".
If we had some decent weather I'd be down on one of the quieter local beaches, stripped off to my knickers, and if anyone happened to be offended by the sight of my 1 and 2/3 breasts (post partial-mastectomy) then they shouldn't be staring.