My hypothesis to explain why today's adults look much younger than adults from decades ago

 Especially the "millennial" generation

Too many chronologically "youngest"??

The perception that today's adults, especially those between 30 and 50, look much younger than their parents and grandparents did at the same age has become quite popular. But if this isn't just an exaggerated impression, then what could be causing this change?

The "media" loves to list changes in habits or culture as the main causes. For example, the way we dress, eat, and other health-related habits would largely explain why today's adults look much younger than adults from 3 or 4 decades ago... Even if these factors have some influence, these differences begin with the very facial structure of today's adults compared to those of the past. An explanation limited to cultural generational differences may not be sufficient, as it could also be a biological phenomenon.

But what would that be?

I bet it's related to the demographic transition and also to cultural habits, but with intergenerational biological effects. I'll explain...

Over the last four or five decades, in many Western countries and some in the East, people have started having fewer children. So, firstly, there has been a reduction in the size of new generations. Secondly, which I consider the most important in my hypothesis, is that, in addition to having fewer children, people also started having them later, starting in their 30s. This is related to the increased mutational load in the human body, as we accumulate more mutations throughout our lives, that is, we age... And since older parents are more mutant, they would be more likely to experience a relative decline in the quality of their reproductive material, sperm, and eggs, resulting in more mutant children (??). But that's not the point, because it may be that youngest children tend to be more neotenic, retaining more childhood traits, both in terms of appearance and behavior. So, with people having fewer children and later, phenotypically "youngest" children, or children born to older parents, would have become more common demographically, including biological characteristics that are perhaps more common in this group. Which, on the one hand, could be a good thing: appearing younger than one's age, but on the other, it could be associated with certain behaviors considered common in new generations, especially adults aged 30 to 50, or "millennials," and not widely appreciated: such as "laziness," individualism, and a more deeply rooted attachment to childhood... a result of their (our?) own "underdeveloped" biologies?? As if we were human "tadpoles" that never quite reach "normal" or "complete" development??

It may also be related to an increase in disorders and diseases due to the increased accumulation of mutations over recent generations. This would explain why there have been more cases of young adults becoming ill and even dying (?).

In any case, unhealthy and assiduously practiced habits, such as smoking and drinking from an early age, having a poor diet, or constant exposure to the sun without any protection, may also have contributed to the premature aging (?) of young adults in previous generations, and new generations have only partially or predominantly reduced the practice of these habits...

Finally, in addition to the factors mentioned, as well as the one I considered the most important for my hypothesis, others could also be considered, such as the prevalence of assortative relationships, in which people are freer today to choose their mates according to their tastes. This, in turn, may have contributed to greater selective pressure for neotenic traits, perhaps associated with more robust sexual selection. (Not just a matter of appearing younger, but also of presenting a more "aesthetically pleasing" appearance.) If, in the past, arranged relationships were much more common and may have contributed to a greater randomness of biological makeup...

But is this supposed or possible phenomenon will it continue to manifest itself in younger generations?

Perhaps not so much, if according to my hypothesis, this tendency to appear younger among "millennials", besides being the effect of a period or demographic transition in which there was an abundance (more in the sense of relative proportion than absolute increase) of "chronologically youngest" children, is also a specific period in the dynamics of intergenerational mutation accumulation, in which the new generations, children of "millennials" and "zoomers" (Generation Z: born between 1994 and 2005ish), would be inheriting/an even greater mutational load, if they are already children of a majority who were born to older parents. So, this possible factor may be contributing to undoing this "spell" of "extended youth" (by appearance) among the youngest, although those who look younger for their age will continue to be relatively more common than in relation to generations much older than them.