I think you gave a biased opinion (as we all do, that's fine). There are plenty of people over 40 in SF [1] and plenty of people who choose to live their full lives here. You may not be friends with them, but they exist.
What I also notice is that most anti-SF people need you to agree SF is bad. They are unwilling to accept that anyone could like it (despite it being one of the most in-demand places to live in America, which they hand wave away as being a jobs thing).
It's truly bizarre, because I comp it to a city like Paris which has many of the same cleanliness & "law and order" problems, but it has nowhere near the amount of people who demand you say it's bad.
[1]https://censusreporter.org/profiles/16000US0667000-san-franc...