> - The lack of control young people experience when it comes to their own lives (voting, etc) will worsen, if the median age is 80+ or older.

This is a really strong status-quo bias shared by many people who are pro-death.

Imagine a world where no one dies, but young people were indeed very sad, depressed, and generally unhappy because of the reasons you stated. Seeing this unfortunate situation, someone says "I have an idea. What if we killed everyone over 82?"

There is an almost infinite number of things you could try that aren't that. The fact that we happen to live in a world where an imperfect partial solution to young people being unhappy is "statistically everyone over 82 dies" doesn't make it a good world; it just means we have to fix unhappy young people in addition to fixing everyone dying.

This critique applies to most of your questions, with the exception of the finitude of resources. But if we can live just until the stars burn out, I'll call that a win over the current situation.