I like the idea of soups and stews too. Anything "hearty" would win my vote, as, in my experience, there is already a glut of places selling pizza, chips, pasta and the ubiquitous baguette.
So, for me: hearty, tasty, small portions. I wouldn't eat a traditional pudding personally, bit no doubt many would.
I think salmon is a good idea too as it can be eaten hot or cold.
I'm not sure your gd has priced quite right for an older market. Would she be prepared to offer to halve the portion size for half the price?
Many older people I know are quite ...um....tight when it comes to eating out.
Or a "special" lunch menu perhaps, comprising a main and sweet, but in a smaller size?
Easier to offer suggestions than to put them into practice, I know!!