1. It won't effect it. Considering that the entire current human population could fit into France or Germany at about the same density as some parts in SE Asia. Not saying this is desirable. But consider how many people could live in the entire solar system? Ultimately in intergalactic space:

https://www.youtube.com/watch?v=gQliI_WGaGk https://www.youtube.com/watch?v=ojEq-tTjcc0

2. Any neuroplasticity loss due to biological aging is itself accumulated damage which will have to be repaired as part of life extension.

3. Human evolution is now overwhelmingly the evolution not of genes but of ideas/culture/memes.

4. That's for an individual to decide. At the moment there are plenty of old people who can apparently think of no reason to live but they hide the fact. They are in effect waiting around to die. They eventually go to hospital and care home for a few years before death which entails a fair bit of suffering and costs a lot of money. This is a sad and somewhat cruel situation in my opinion.

5. I bet that the cheapest way to treat things like heart disease and cancer will turn out to be life extension technology (i.e. damage repair). So you may have to decide not to get treatment for things which are currently routinely treated by conventional means. Of course you might still fall down the stairs...