Where a season’s length is determined by the time from solstice to equinox, the length of each lifecycle phase is determined by the span of time between birth and the coming of age into young adulthood. In American society, the ritual acknowledgment today occurs at 21, the age of college graduation and initial career launch. Afterwards, a person is deemed to be an autonomous adult. The length of life’s first phase fixes the length of the other life phases as well. Once one batch of children has fully come of age, it and it alone comprises the society’s young adults, casting its next-elders into a midlife social role. This now happens when the latter reach age 42, the minimum age U.S. history (though not the Constitution) has declared acceptable for a President. And, in turn, the group entering midlife pushes another into an elder role, now starting around age 63, today’s median age for receiving one’s first old-age benefit check from government.

Since the share of people able to survive the elderhood phase of life has grown enormously over the last fifty years, it may make sense to define a new phase of life: late elderhood (age 84 on up). The social role of late elders is pure dependence, the receiving of comfort from others.

The phases, and social roles, of the modern American lifecycle can be summarized as follows:

• Childhood (pueritia, age 0–20). Social role: growth (receiving nurture, acquiring values).
• Young Adulthood (iuventus, age 21–41). Social role: vitality (serving institutions, testing values).
• Midlife (virilitas, age 42–62). Social role: power (managing institutions, applying values).
• Elderhood (senectus, age 63–83). Social role: leadership (leading institutions, transferring values).
• Late Elderhood (age 84+). Social role: dependence (receiving comfort from institutions, remembering values).

The first four (childhood through elderhood) comprise the quaternity of the human lifecycle. The length of these four—roughly 84 years—matches the span of the American saeculum dating back to the Revolution.