Their theory, they get to make the parameters. Only applies to USofA:
Generations by year of birth according to Strauss–Howe
Late Medieval Saeculum
Arthurian Generation (1433–1460) (H)
Humanist Generation (1461–1482) (A)
Reformation Saeculum (104 years)
Reformation Generation (1483–1511) (P)
Reprisal Generation (1512–1540) (N)
Elizabethan Generation (1541–1565) (H)
Parliamentary Generation (1566–1587) (A)
New World Saeculum (112 years)
Puritan Generation (1588–1617) (P)
Cavalier Generation (1618–1647) (N)
Glorious Generation (1648–1673) (H)
Enlightenment Generation (1674–1700) (A)
Revolutionary Saeculum (90 years)
Awakening Generation (1701–1723) (P)
Liberty Generation (1724–1741) (N)
Republican Generation (1742–1766) (H)
Compromise Generation (1767–1791) (A)
Civil War Saeculum (67 years)
Transcendental Generation (1792–1821) (P)
Gilded Generation (1822–1842) (N)
None (Note 1) (H)
Progressive Generation (1843–1859) (A)
Great Power Saeculum (82 years)
Missionary Generation (1860–1882) (P)
Lost Generation (1883–1900) (N)
G.I. Generation (1901–1924)[28] (H)
Silent Generation (1925–1942)[29] (A)
Millennial Saeculum (age 74 years in 2017)
Baby Boom Generation (1943–1960)[30] (P)
Generation X (1961–1981)[31] (N)
Millennial Generation (1982–2004)[32] (H)
Homeland Generation (2005–present)[33] (A)
Key: Prophet (P), Nomad (N), Hero (H), Artist (A)
https://en.wikipedia.org/wiki/Strauss%E2%80%93Howe_generational_theory