Vishnu Puranam is 23,000 verses into Six Cantos. It describes the Ashrama Dharamas - there are Four Ashramas : Brahmacharya Ashram, Grahastha Ashram, Vanaprastha Ashram and Sanyasa Ashram to be followed by a man.
According to Bavishya Puranam - Yajnopaveetham(threading ceremony ) - For a Brahmin Boy should be performed before Eight Years. Eleven Years for a Kshatriya Child and Sixteen for a Vaishya child. An Unmarried Man should wear 3 threads of Yajopaveetham and it becomes Six for a Married Man.
During Brahmacharyashrama, immediately after the Yajopaveetham , the child has to be sent to attend lessons on Veda under the custody of a Guru (a learned scholar). He should listen to his Guru as long as he is with him. He should pay respect and obeisance to the Guru and keenly follow all the instructions by him. During this period, the child has to attend Guru's commands and follow him with utmost respect. Duties involved are the daily rituals, reciting Veda and attending all the requirements of the Guru . When the Guru is thoroughly convinced about the knowledge of the child, when he attains the maturity, the boy is sent for the next Stage - Grahasthashram.
During Grahasthashrama, getting married and earning livelihood as described in the Puranas. Serve the God through Sacrifices and daily rituals, Serve the Guest with food and shelter, Serve the Rishis by reciting Vedas, Serve Lord Brahma by producing children of good virtues and finally serve the entire world with Truthfulness. An Unhappy guest leaves all his/her sins with the householder and takes away the good karmas of householder . Many years of completing the Grahasthashrama after fulfiling the entire responsibilities, a person leaves for Vanaprastha.
Vanaprastha is the third stage of leading life as a forest-dweller. At this point of time, he leaves the entire wealth to the heirs and leaves to the Forest. He can be followed by his wife or can leave under the custody of his children. He lives in the Forest (hermitage), eats fruits to waive off hunger, leaves all the comforts behind and devotes his time to Meditation. During this period, he keeps away from all the actions like cutting hair , shaving beard , etc..
At the final stage of Sanyasashram he is ready to leave his children, wife and all material possessions absolutely. He keeps moving from one place to another, performs Yoga (to make a communion with the God), he never stays more than one night in a village and five nights in a city. A final journey in search of 'BRAHMAM'.
Jai Sriman Narayana !!