R' Shneur Zalman of Liadi writes in Iggeres HaTeshuva that
But even if one has incurred excision or death, there yet remains an impression within him of his Divine soul, and through this he may live until fifty (in the case of excision) or sixty years (in the case of death by divine agency), but no more.
In the next chapter, however, he says that
However, all this obtained when Israel was on an elevated plane, when the Divine Presence dwelt among Israel1 in the Beit HaMikdash. Then the body received its vitality only through the divine soul, from the innermost source of the life-giving power issuing from the Infinite One, through the Tetragrammaton, as discussed above. But they then fell from their estate, and through their actions brought about the mystic exile of the Divine Presence, This means that the benevolence flowing forth from the above-mentioned latter hei of the Tetragrammaton was lowered far down, from plane to plane, until it became enclothed in the Ten Sefirot of nogah, which transmit the benevolence and vitality through the hosts of heaven and those charged over them, to every living physical being in this world, even to vegetation, as our Sages state: “There is no blade of grass below that has no spirit [Above that smites it and commands it: Grow!]” Hence, even the sinful and deliberate transgressors of Israel may receive vitality [from it] for their bodies and animal souls, exactly as other living creatures do...
Hence the statement of our Sages, of blessed memory: “It is not within our hands (i.e., it is not given us) to understand the reason for either the tranquillity of the wicked [or the suffering of the righteous].” The quotation specifies “in our hands,” i.e., in this time of exile after the Destruction
In other words, there is a spiritual system laid out in the Torah - Do mitzvos and get a reward. Do aveiros and get punished. It worked in the time of the Beis Hamikdash as our physical life and sustenance was given through the "direct flow" of G-dliness. Therefore, someone that was punishable for the death penalty in the heavenly court would die right away, as he had no source from which to live. However, nowadays we are in exile, and not just physically but also spiritually. Therefore, our life-force comes through the impure-side (which gets its life-force from the Makkif [the G-dly light which comes through without limitations]). Therefore, we do not always have a correlation between doing mitzvas and reward (and lack of mitzvas and lack of reward).
