When you reach a certain age, everybody around you who apparently shows concern on your well being will give you unsolicited advice asking you to slow down and take things easy, that now is the time to the fruit of your labour and the sweat of your hard work. They would often quote you instances and examples of apparently healthy individuals just dropping dead like flies after a seemingly trivial chore. The way they coax (or put you in a corner), they seem to be cocksure of their facts and pretty soon plant the recurrent seed of doubt, uncertainty and fear in your brain. Admittedly, no matter how much there is of better living condition in the afterlife, we rather grow old, sick, wasted, unwanted and shoved around than die no time sooner, preferably never!
You will slow down, fearing for the worst, the unknown enemy. You become sluggish, puffed up, unfit and fat, poorly coordinated and a ticking time bomb. When your pin is unhooked, you disappear, become another statistic and everyone will move on with life, looking out to dash the hope of another health conscious middle aged man.

Man would not have reached where he has reached now if he had stayed in his comfort zone, fearing the unknown. There would not be any of our ancestors who would have walked out of the African continent to explore newer pastures, no tomatoes in Indian cooking as tomatoes are native of Mediterranean land, no spices in cooking (the European wanted to find alternate route to lay their hand on these black gold), no preserved foods until refrigeration came around, no pleasures of smoking as the the first puffer would have been petrified to inhale, no simple pleasures in life (scared of retribution in afterlife), no new World as we know it as Columbus would have been stiff dead to topple over at the edge, no Fauja Singh running till the age of 101, no Arnie and no Arnie for post of Governor of California if he were just contented with green card, no space exploration, above us only sky, do not incur the wrath of the unknown force...
True, everybody has their potential and threshold. No pain and no gain they say. You certainly do not want to push yourself to the limits and beyond and to realise too late for goodbyes. It is an art to know your limits. Use the sciences and the signs to reap the maximal benefit out of activities.

I remember hearing a story in my childhood. A sage meditated for months to get his wish granted. He did not want to drop dead but to be given ample warnings. The Gods agreed.
The sage lived close to a century and died in his sleep. In heaven, he questioned the Gods for not keeping to their words. The Gods, in reply, denoted that They kept their side of bargain! The greying, receding hairline, the kyphosis, the joint pains, the reduced effort tolerance, the failing eye-sight, the slow thinking processes and so on.... The sage, the wise one he had been, had failed to notice!