On a lighter note, I can imagine that the size of the ego which accompanies the type of person that lives to 9,000 years old would more than likely encourage someone to poison or strangle them.
The world where life span runs on like that is deeply, profoundly weird, and thinking about it is hard because it's so unlike where we live. You can't just imagine one 9,000-year-old and try to imagine what the world is like, because they will not be alone.
I mean in the current world rich assholes do eventually die and sometimes their replacements are better (or worse, but in a way that destroys their power base). Do you really want to live in a world where the Bilderberg Group is immortal?
But there's a reason we use the word "singularity" to describe that kind of future- it really is impossible to envision with any greater accuracy or confidence than elizabethans could imagine the world of 2016.
At that point the crystal ball becomes too fuzzy for me to guess exactly how they will react, except to point out that "go kill all the old people" is a really uncreative solution to the problem, and you've got a lot of people who will be highly incentivized to find another solution, since they plan on being the old people at some point.
Except everyone (the majority) could be old people too.
If you can live for 5000 years for example, you don't need as many reproduction going on (besides the huge overpopulation that would already be going on).
It is possible that human mentality would change if we had to start thinking about longer timescales like this, but that seems optimistic.