Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 43


नारद उवाचइति तौ दम्पती तत्र समुद्य समयं मिथ: ।तां प्रविश्य पुरीं राजन्मुमुदाते शतं समा: ॥ ४३ ॥


nārada uvācaiti tau dam-patī tatrasamudya samayaṁ mithaḥtāṁ praviśya purīṁ rājanmumudāte śataṁ samāḥ


The great sage Nārada continued: My dear King, those two — the man and the woman — supporting one another through mutual understanding, entered that city and enjoyed life for one hundred years.


One hundred years is significant in this connection because every human being is given the concession to live up to a hundred years. The span of life is different on different planets, according to the planet’s distance from the sun. In other words, one hundred years on this planet is different from one hundred years on another planet. Lord Brahmā lives for one hundred years according to time on the Brahmaloka planet, but one day of Brahmā is equal to millions of years on this planet. Similarly, the days on the heavenly planets are equal to six months on this planet. On every planet, however, the span of life for a human being is roughly one hundred years. According to the life spans on different planets, the standards of living also differ.