Sutton would be fine except for the Winthrop problem, but even with a 30-year old Marian it's weird to me she has a 10-year old brother. But if she's under 30 the sense of her being an old maid evaporates.
In 2020, yes; in 1912, no. Marian is probably meant to be about 25, give or take. In a small town at the beginning of the last century, an unmarried woman of 25 who didn't even have the ghost of a boyfriend anywhere in sight was definitely considered on the road to old-maidhood, at least. Where was she supposed to get a husband from, if she hadn't got one already by that age? It's not as if she were in New York, or even Chicago, and could just step out and take her pick from among the teeming hordes. It's probably why there were so many jokes in those days about farmer's daughters and "traveling salesmen."