هُوَ الَّذِى جَعَلَكُمْ خَلَـئِفَ فِى الاٌّرْضِ

(He it is Who has made you successors generations after generations in the earth,) meaning, all people succeed one another, generation after generation. This is like the Ayah:

وَيَجْعَلُكُمْ حُلَفَآءَ الاٌّرْضِ

When the people in Jahannam will plead with their Lord that they be delivered from its punishment, so that they could do good deeds then, and not do the bad ones they did earlier, at that time they will be told: أَوَلَمْ نُعَمِّرْ‌كُم مَّا يَتَذَكَّرُ‌ فِيهِ مَن تَذَكَّرَ‌ وَجَاءَكُمُ النَّذِيرُ‌ "Did We not give you an age in your life in which lesson could have been learnt by the one who wished to take lesson - 37) Sayyidna Ibn Husain Zain ul-` Abidin رضی اللہ تعالیٰ عنہ said, "It means the age of seventeen years." And Qatadah (رح) gave the age as eighteen years, meaning thereby the age of puberty. And the difference of seventeen and eighteen is possible in determining the age of puberty, as someone may reach puberty at the age of seventeen and someone else at, eighteen. In the Shari'ah, the age of puberty is the first line of demarcation after having crossed which a person is Divinely blessed with enough reason, so that one can understand what is good or bad in his or her case. Therefore, this address will be to disbelievers at large irrespective of their ages being long or short. However, the one who had a long lease of life, yet did not come to his senses, saw all sorts of physical proofs scattered around and heard the teachings of the prophets, still did not recognize the truth - so then, this one will be more blameworthy.

In short, the person who saw nothing beyond the age of puberty, he too was given enough power of discrimination by nature that he could have used to distinguish between the true and the false. When he failed to do that, he too is deserving of censure and punishment. But, the person who was given long years to live, the warning of Allah stood served against him in a more conclusive degree. Then, if he could still not shake off his disbelief and disobedience, he would be more deserving of punishment and blame.