Technically there should be a ratio of young to old to take care of all of the elderly

That’s a rule of thumb that assumes a lot of things about elderly people’s need for care, how much that’s funded by the young, productivity in how that care is provided, and a huge number of other variables.

Lower population will make resource allocation easier and improve quality of life, and obviously is necessary to prevent further environmental damage.

The environmental damage is more to do with bad choices about the mix of technology currently used to power the economy, and the poor ratio of GDP per unit of energy consumed. So I dispute that “obviously.”