Disease isn't even the half of it. As you age your body simply wears out. Your muscles begin to wear out and break down, eventually including critical ones such as your heart, your bones become frail to the point that even slight fall becomes potentially lethal, and of course as I assume you were alluding to - your mind also begins to give way such that even if you might still have a heart beat, you're hardly alive. Imagining all of this will suddenly be overcome is neither rational nor in any way supported.

Individuals like Ray Kurzweil intentionally lied to themselves. His argument was that human life expectancy has been increasing rapidly over the past 'xx' years, and eventually it will accelerate to a rate such that life expectancy will increase by more than a year, per year - immortality. But it's just complete and utter nonsense. Life expectancy increased largely because of reductions in infant mortality - not people living longer. And he certainly knows that. Individuals like Hippocrates (of the Hippocratic Oath) lived to their 90s 2,400 years ago. The peaks of human longevity aren't changing much at all. The only thing that's changing is that more people are able to get to them.