I really enjoyed this article by Oliver Lee Bateman, Should Millennials Ever Grow Up?. It lies directly the sweet spot in the perennial arguments over generational categories and life-stage judgementalism.
But childhood, far from being some mythical status existing from time immemorial, was actually a historically contingent stage. For most families, children were once units of labor, tiny adults who could be employed on the farm or, following industrialization, in mills and factories. In Pricing the Priceless Child: The Changing Social Value of Children, Viviana Zelizer demonstrated how legal changes gradually removed children from the workplace, as the nation’s growing affluence enabled mass-scale education and sentimentalization of the young, even as the need to keep these priceless babes (fewer in number than ever before, since quality now mattered more than quantity!) supplied with toys also led to an increasing “monetization and commercialization of children’s lives.”
With a healthy dose of historical context, and a resistance toward over-categorization, it’s possible to understand age and maturity as highly variable. Some children grow into adulthood more quickly, by chance or by need. Some people never really mature at all.