I agree that late-modern adults can be childlike. I call this the infantilization thesis, and I've written it up in the articles below. So how can I argue both that consumerism infantilizes us, and that history maps onto this metaphor of individual growth? Because the latter is extremely broad, whereas consumerism and infantilization are narrower in applying mainly to the top ten percent of developed countries.
Moreover, we can afford to be infantile consumers only because we defer to experts in running our high-tech world. So our infantilization presupposes a greater degree of relative adulthood that's distributed elsewhere in our collective. By contrast, in prehistory there was no such high-tech society to run, so that's why they could afford to be childlike: because they had less to lose and because they hadn't yet accumulated much knowledge (beyond what was needed for their survival as hunter-gatherers and early townspeople).
