Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 1

Sanskrit:

श्रीभगवानुवाचवनं विविक्षु: पुत्रेषु भार्यां न्यस्य सहैव वा ।वन एव वसेच्छान्तस्तृतीयं भागमायुष: ॥ १ ॥

ITRANS:

śrī-bhagavān uvācavanaṁ vivikṣuḥ putreṣubhāryāṁ nyasya sahaiva vāvana eva vasec chāntastṛtīyaṁ bhāgam āyuṣaḥ

Translation:

The Supreme Personality of Godhead said: One who desires to adopt the third order of life, vānaprastha, should enter the forest with a peaceful mind, leaving his wife with his mature sons, or else taking her along with him.

Purport:

In Kali-yuga a human being generally cannot live more than one hundred years, and even this is becoming most unusual. A man who has a reasonable expectation of living for one hundred years may adopt the vānaprastha order at the age of fifty, and then at the age of seventy-five he may take sannyāsa for complete renunciation. Since in Kali-yuga very few people live for one hundred years, one should adjust the schedule accordingly. Vānaprastha is intended as a gradual transition from materialistic family life to the stage of complete renunciation.