Technically, a short lifespan almost always means high childhood mortality. Once you make it to adulthood, there are still plenty of ways to die, but they're not as likely as people think. Humans are tough.

So, no, nature doesn't want you dead at 50. 60-70 is when nature *wants* you dead. Before then, it'll gladly kill you if you give it half a chance, and that includes doing many day to day activities when the dire dice of destiny are about to land with both sixes down.