Shashti Poorthi is celebrated on completion of 60 years of age of the male. This term is derived from Sanskrit in which Shashti means sixty; abda–year; poorthi-completion. It marks completion of half the years of one's lifetime as in Hinduism, 120 years is considered the life span of a human being. The sixtieth year in one’s life is a significant milestone, memorable turning point, a touching reminder of the rich, mellowed life that would unfold in the years to come.
In fact, the Hindu calendar has 60 years (named Prabhava, Vibhava, etc.) that repeat themselves after every 60 years in a sequence. Shashti poorthi marks the completion of one such cycle. For example, a person born in the year Pramodootha and has lived for 60 years will have seen all the 60 years in the calendar. This milestone marks celebration and gratitude for life given by God. So once his birthday arrives in Pramodootha year, he performs his Shashti poorthi.
In recent days, children started doing this ritual to their parents, just as their parents performed all of their rituals in their childhood.One more important aspect of Shashtiabdha poorthi is that all the planets in the zodiac come to the same positions or occupy the same houses of zodiac as compared to the actual date of birth of the individual. These planets take the same position as they were on the date of birth of the individual after 60 years.