ישעיהו, פרק ס״ה, פסוק כ׳

In the days of the Messiah, human existence will undergo a dramatic transformation. Life expectancy will return to the vast, extraordinary lengths experienced at the very beginning of the world, during the generations from Adam to Noah. Within Jerusalem and the Land of Israel, premature death will become a thing of the past, and no one will be carried out for an early burial [רד״ק, מצודת דוד].

The primary approach among commentators is that young children will no longer succumb to illness or sin, and older adults will not pass away from natural weakness before living for hundreds of years [מלבי״ם, אבן עזרא, רד״ק]. Another perspective suggests that this promise addresses the tragedy of premature aging. Rather than speaking of a child and an elder separately, it describes a single individual who is chronologically young but appears elderly due to the early onset of physical decline. In the future, this heartbreaking phenomenon will completely vanish [שד״ל].

This monumental change in longevity will also shift how society perceives age. If a person were to pass away at the age of one hundred, people would consider them a mere youth who died tragically early. At a century old, a person's mind will not even be considered fully mature when compared to the immense lifespans of that era [אבן עזרא, רד״ק, מצודת דוד, ביאור שטיינזלץ].

This extended lifespan will also alter the divine standard for punishment. There are three main ways to understand the fate of a sinner who reaches the age of one hundred. The first approach explains that the threshold for accountability will change. Unlike the current reality where a person faces punishment for sins committed in their youth, in the future, an individual will only become liable for a heavenly death penalty starting at the age of one hundred [רש״י, מלבי״ם, ביאור שטיינזלץ]. Furthermore, this condition hints at offenses severe enough to warrant excommunication [רש״י]. A second view explains that passing away at one hundred will be seen as a sudden absence and a divine curse. Because this age will be considered so young, it will be obvious to everyone that the person's early departure from the world was a direct result of their sins [מצודת ציון, מצודת דוד, רד״ק]. A third approach understands this as a literal curse spoken by people. When seeking to curse a wrongdoer, the most severe fate society will be able to wish upon them is that they should die young by passing away at the age of one hundred [שד״ל].