Various studies on happiness have indicated that the
worst age is one's 40s; being younger on average entails more interesting experiences, while senior citizens often enjoy a peak of happiness relating to retirement, lack of responsibilities and the wealth to travel and socialise endlessly.
Since society is dynamic, though, I see this shifting over the coming decades. Firstly, the average age that people live is currently increasing markedly. In Australia, just a few years ago it was 70-something, now it's 80-something. Based on this trajectory, a young person alive today would surely be expected to live beyond 100 or even 110. This new context would make a 70-year-old quite young by comparison.
Of course, that estimation doesn't account for population declines caused by wars, famines, environmental calamities and, heaven forbid, an exodus of suffering people via legalised voluntary euthanasia. Conversely, young people today may not have the same abundant opportunities for long-term stable employment, lifelong marriages, active families, affordable property, ample retirement funds and other factors that set up the previous generation for a utopian (aside from health issues) ageing high-point.
My personal experience, as a 40-something, abandoned/low-status member of society, has been less than stellar. In order to address the fear of homelessness, I had to work stupid hours on crappy jobs, putting on a fake smile and fighting fatigue and poor mental health all the way. Eventually, this obsessive effort ticked a basic box since I now have a house, but in the years that have passed, I've accelerated health problems through living under constant stress, have barely scratched the surface of dealing with trauma, and the lifelong dream of finding a partner gets more and more distant as the first signs of greying and balding become apparent. Right now, I have again delayed plans to actually CTB by a few months, but will not be giving up my N from D any time soon.