One Manu lives for a duration of time calculated to be an aggregate of seventy-one yuga cycles, each of which equals 4,300,000 years. Although atheistic men like to enjoy material opulences and they endeavor with great energy to build big residences, roads, cities and factories, unfortunately they cannot live more than eighty, ninety or at the utmost one hundred years. Although the materialist exerts so much energy to create a kingdom of hallucinations, he is unable to enjoy it for more than a few years. However, because Prahlāda Mahārāja was a devotee, the Lord allowed him to enjoy material opulence as the king of the materialists. Prahlāda Mahārāja had taken birth in the family of Hiraṇyakaśipu, who was the topmost materialist, and since Prahlāda was the bona fide heir of his father, the Supreme Lord allowed him to enjoy the kingdom created by his father for so many years that no materialist could calculate them. A devotee does not have to desire material opulence, but if he is a pure devotee, there is ample opportunity for him to enjoy material happiness also, without personal endeavor. Therefore, everyone is advised to take to devotional service under all circumstances. If one desires material opulence, he can also become a pure devotee, and his desires will be fulfilled. It is stated in Śrīmad-Bhāgavatam (2.3.10) :

akāmaḥ sarva-kāmo vā mokṣa-kāma udāra-dhīḥ tīvreṇa bhakti-yogena yajeta puruṣaṁ param

“Whether one desires everything or nothing, or whether he desires to merge into the existence of the Lord, he is intelligent only if he worships Lord Kṛṣṇa, the Supreme Personality of Godhead, by rendering transcendental loving service.”