Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 42

Sanskrit:

तत: परिणते काले प्रतिष्ठानपति: प्रभु: ।पुरूरवस उत्सृज्य गां पुत्राय गतो वनम् ॥ ४२ ॥

ITRANS:

tataḥ pariṇate kālepratiṣṭhāna-patiḥ prabhuḥpurūravasa utsṛjyagāṁ putrāya gato vanam

Translation:

Thereafter, when the time was ripe, when Sudyumna, the king of the world, was sufficiently old, he delivered the entire kingdom to his son Purūravā and entered the forest.

Purport:

According to the Vedic system, one within the institution of varṇa and āśrama must leave his family life after he reaches fifty years of age (pañcāśordhvaṁ vanaṁ vrajet). Thus Sudyumna followed the prescribed regulations of varṇāśrama by leaving the kingdom and going to the forest to complete his spiritual life.