As you get older your arteries gradually narrow, a process made even more severe by the buildups of plaque. This is all accelerated by obesity, lack of exercise

As you get older your arteries gradually narrow, a process made even more severe by the buildups of plaque. This is all accelerated by obesity, lack of exercise, and so on. Aging, high blood pressure, and various other factors also causes arteries to weaken, making a rupture even more likely. All of this is part of the reason I think the 'search for the pill/shot of immortality' in modern times is little different than the search for the pool of immortality in ancient times. Everything breaks down over time and so to solve this, we'd need to fix everything, when we yet struggle to truly fix even a single thing.