The Scumbag 2nd law of thermodynamics is a really harsh mistress (Solved ageing? Die of cancer anyway etc.).
But hey, the digerati elite are showing touches of grey and most of them wouldn't have any better use for their money anyway once they've got the mansion, the yacht, the jet, and the mistress(es) half their age.
Every time a cell divides, it has a chance of turning malignant. Live long enough and one of those cells will win the cancer lottery and take you down if you don't catch it in time. Many forms of cancer are symptom-free long enough for this to happen (pancreatic for example) and we do not yet have the technology to easily detect this until it's late in the game.
And that's just one way to go. Then there are aneurisms and all sorts of other odd bodily defects that will eventually manifest.
Ageing is tough. That said, eat right, exercise, and get enough sleep, and you'll stand the best chance to max out your time clock.
Anyway, some people like to work on tough problems. No one said it's going to be easy or that progress won't come slowly. There are 7 billion people on the planet. If you can help with early detection of pancreatic cancer, for example, you will impact many lives.
What happens when we get good at treating dementia?
(Obviously, "good at treating" is with respect to what went before, not where we want to be.)
What happens when we get good at treating dementia is that your children will be able to have intelligent conversations with their great great grandparents (or you will be able to have intelligent conversations with your great great grandchildren).