Outside of the USA noone knows what idk, 50°F feels like. Probably around room temperature since you say it's based on how humans feel but I have no idea.
Anyone who gets surprised when they find out someone has never been skiing.
That depends on culture a lot. In Austria it's actually rare to find someone who has never been skiing (25% of the population go skiing regularly, and that has already been at around 50% not many years ago). Even when not doing it with your family while growing up everyone learns it at school.
I'm not rich at all but I do get surprised when someone who isn't obviously from another country has never been skiing (typically it means that they grew up somewhere else but you just don't notice anymore).
I meant it's shrinking without immigration, yes. As more and more countries are developed, less and less countries have population growth, so there's also no population growth through immigration anymore (when one time the people from the few countries that still have population growth are distributed among so many countries without population growth).
It is solving itself if we keep working on helping countries to become developed.
They should, yes. Children are extremely important for our future so especially people who earn well and can provide their children with a good life (likely leading to a successful carrier later on) should be encouraged to have them.
Additionally this kind of culture is needed if we want women to have same chances as men (since childcare still is majorly done by women, and likely always will be (progressive families split it evenly, conservative families don't or at least don't split it evenly, for every family where the father does more there's at least one where the mother does more))
At my uni I recently met two people in their mid 40s to 50 (eyeballing) who started mechanical engineering this year. It's never too late.
And a friend who's studying medicine said a group of people in their 50s started a year ago