Many shabads in the Siri Guru Granth Sahib talk about the stages of life in terms of the “aath paharay”—eight periods of three hours each during the course of the day and night. This divides the lifespan of a human being into four parts, which is why many shabads in the Siri Guru Granth Sahib talk about the “four watches.”
These shabads often describe the comparison between someone who lives consciously versus unconsciously. In this way, Sikhs are reminded to live life to the fullest by remembering God and living each divine moment, each “pahar” or “watch” in the most conscious way possible.
The Siri Guru Granth Sahib doesn’t talk specifically about the ages associated with each watch. However, it can be deduced that the first watch could be interpreted as approximately 0-3 years old, the second watch as about 4-14 years old, the third watch as roughly 15-35 years old and the fourth watch as about 35-50 years old. It is important to note that in the time of the Gurus, life expectancy was about 50 years old.
~ Information shared with SDI by MSS Hari Dharam Kaur Khalsa