Death and lifespans are part of the will and decree of Allah that He wrote in al-Lawh al-Mahfooz with Him, fifty thousand years before He created all of creation. That is not subject to change or alteration; Allah, may He be glorified, wrote it according to His knowledge that cannot cannot be changed without Allah's will.
وَأَنْفِقُوا مِنْ مَا رَزَقْنَاكُمْ مِنْ قَبْلِ أَنْ يَأْتِيَ أَحَدَكُمُ الْمَوْتُ فَيَقُولَ رَبِّ لَوْلَا أَخَّرْتَنِي إِلَىٰ أَجَلٍ قَرِيبٍ فَأَصَّدَّقَ وَأَكُنْ مِنَ الصَّالِحِينَ- وَلَن يُؤَخِّرَ ٱللَّهُ نَفْسًا إِذَا جَآءَ أَجَلُهَا ۚ وَٱللَّهُ خَبِيرٌۢ بِمَا تَعْمَلُونَ-
And spend [in the way of Allah ] from what We have provided you before death approaches one of you and he says, "My Lord, if only You would delay me for a brief term so I would give charity and be among the righteous." But never will Allah delay a soul when its time has come. And Allah is Acquainted with what you do. (Surah 63:10-11)
That does not mean that death and lifespans are not subject to the laws of cause and effect that Allah has created in this universe; rather the issue of death, like anything else that is decreed in this world, is based on tangible causes that were also written in al-Lawh al-Mahfooz.
For example, The one who wants to memorize the Qur’an – for example – should take appropriate measures in order to achieve that, such as reading, revising, listening, repeating and so on. If he takes all appropriate measures, he will be able to memorize it, but if he falls short in that, he will not attain what he wants. The knowledge of Allah, may He be exalted, from eternity encompasses all that will happen to this individual. Allah, may He be glorified, knows whether he will strive to memorize and recite, or will fall short in that, and He commanded that what is known to Him should be written in al-Lawh al-Mahfooz with Him, may He be glorified, and His knowledge is not subject to any error.The same is applicable to death: it has physical causes which are known to all people, such as falling from a great height, or a deep wound in the body of a fighter, or grave illnesses, and the like. And there are tangible measures that could delay or postpone death, such as taking care of one’s health, keeping away from dangerous places and situations, and so on. There are also intangible measures which the Prophet (blessings and peace of Allah be upon him) told us may increase our lifespan, such as du‘a’ (supplication), upholding ties of kinship, honoring our parents, and all other righteous deeds.
Whoever takes such measures will deserve an increase in his lifespan, and whoever falls short in taking appropriate measures to preserve life is exposing himself to death. All of that – whether cause or effect – is known and written with Allah, may He be exalted, from beginning to end, and cannot change, because it is known to Allah how it will unfold, regardless of what man changes in the measures that he takes.
The pens have been lifted and the ink has dried (At-Tirmidhi, 2516) So, keep the faith strong,turn to Allah, and trust Allah alone.
In the Name of Allah Most Merciful, Most Beneficent in Mercy, All praise is due to Allah, and may the peace and blessings of Allah be upon our leader, the Messenger of Allah, and upon all his family and upon his companions, To proceed 4 compulsory things a Muslim must know are -
1. The first is knowledge, which is the knowledge of Allah, the Almighty and Majestic, the knowledge of the Prophet, and the knowledge of the religion of Islam. It is not allowed to worship Allah with ignorance since whoever does this is astray.
2. The second is action, since the person who has knowledge but does not inmplement it has evoked Allah's anger, as they had knowledge but did not act accordingly. One of the deceptive enticements of Satan is that he discourages people from gaining beneficial Knowledge by deceiving the person into thinking that he is excused by Allah due to his ignorance. What this person does not realize is that if he deliberately stays away from learning while he has the ability, the proof is established against him (for punishment). This is the trick that Satan played upon the people of Noah, as Allah mentioned in the Qur'an when they:
"put their fingers in their ears and covered themselves with their clothes"
..in order to plea that the proof would not be established against them.
3. The third is calling and propagating the knowledge and practice of Islam, for the scholars and callers are the inheritors of the Prophets. Allah the Exalted cursed the Israelites because they used to forbid others the wickedness that they themselves would do, and what an evil thing they did. Teaching and calling to Islam is a community obligation, and thus when some of them fulfill this obligation none are blameworthy, but if all leave it, all are blameworthy.
4. The fourth is to have patience and perseverance with any misfortune faced in learning, practicing, teaching and calling others to it.
As it is said, if something cannot be attained in its fullest, one should not neglect what can be attained of it. If what we say is correct then it is from Allah, and if what we say is incorrect then it is from ourselves and Satan, and Allah and His Messenger are absolved and cleared from it.
Rest Allah knows best.
Source: Quran, Sunnah, Islam QA, An Explanation of the Last Tenth of the Noble Qur'an [Also with Critical Matters in the Life of a Muslim] Paperback – 2007; www.tafseer.info