Is there a tendency in society to assume that a woman "must" want a husband and children, and is somehow failing and pitiable if she doesn't have that? Historically and generally, absolutely yes - but I don't see it strongly now in my own social and professional circles. I think it's more and more acceptable to make all different kinds of choices. So, I'd feel sympathy with your colleagues and family members if they're feeling singled out and having negative assumptions made about them - but I'd mainly be judging the assumption-makers for being a bit narrow-minded.
I come from a pretty traditional and conservative (and extremely religious) culture, but even there things are changing. There definitely are "attitudes" - my sister is single and outspokenly childfree (and a lesbian) and while our parents are supportive, I know extended family and older family friends and neighbours find it oddish. I also think about a fortyish single friend/colleague who grew up in the US with Japanese-born parents. Her grandmother warned her very seriously that unwed women over the age of 24 are called "old Christmas cake" in Japan - but her parents and siblings think that's hilariously funny, not realistic. I think things are more open-minded in the UK - my (Scottish) SIL has two children who are the centre of her world, but hasn't been "in a relationship" in over a decade and she seems really happy; anyone feeling sorry for her doesn't know her well!
There are also a LOT of variations in life paths - one person may couple up (or not) and have children young and then enjoy her forties with the partner long gone and the children semi-independent. Another may stay single and childfree and then couple up later and even end up with an unexpected family - I was just reading that Kamala Harris, for example, got married for the first time at 49 and ended up with two teenage stepchildren. (And I do kind of wonder: would Americans be happy with a completely single woman VP or President; no first or second gentleman?) And some people never do either, and don't miss or want it. So I'd say fortyish might be a touchy age for someone who wants and doesn't (yet) have children - but for childfree people and/or relationship-wise, not really a bigger deal than any adult age.
Also: when I hear the word "spinster", I just think of the social media website started by MK Fain, an American woman who decided to offer an alternative after being kicked off Twitter for being too outspoken. "Spinster" is a very cool concept, as long as you embrace it. 