I'm surprised that none of the studies mentioned in this article (and there were a lot) talk about potential differences by age. I think this is pretty critical

I'm surprised that none of the studies mentioned in this article (and there were a lot) talk about potential differences by age. I think this is pretty critically important for 2 main reasons: 1. People want different things at different stages of life, and a situation that could be a boon at one stage could be a burden at another. E.g. one hypothesis is that raising kids by a married couple can be exhausting and stressful while single people are going out and having fun, but then once those kids are out of the nest that the married couple is more fulfilled and happy than their single counterparts. Obviously that's a somewhat stereotypical hypothesis - my only point is that life stage matters, and it's possible that married couples may be happier than singles at some life stages but not at others. 2. Age matters because societal attitudes have changed over time. My parents grew up in an era where the expectation was that everyone got married, and if you didn't, something was "wrong" with you. So it's possible that single people from older cohorts really are outliers compared to their peers. As times have changed, societal attitudes have allowed being long-term single to be more of a choice, and especially in countries like Sweden you see marriage as no longer being the "default" option.