I don’t know why older people tend to carry more weight, but it seems to me that it was ever thus. Both my grandmothers were overweight. My mother was a slim young woman, as was her sister, but both put weight on as they grew older. My sister was thin as a young woman, but she’s not thin now. The same for me, I was an extremely slim young woman, but am not an extremely slim older woman. I’m not obese, but my BMI is perilously close to tipping into overweight.
There are many reasons why people of all ages are overweight, but older women have often put on weight as they age. Fewer hormones, possibly less exercise, less running around after children, maybe more car use. Who knows, but it seems to have been always the case.
And judging by threads on what Gransnetters eat, I would say most of us eat a reasonably healthy diet, and mostly home cooked.