The most important thing one can do to avoid looking old is to avoid the sun. Sun makes skin wrinkly: https://www.cbsnews.com/news/trucker-accumulates-skin-damage.... Folks today generally spend less time in the sun than they did a few decades ago. The smoking also probably played a part in people making look old long ago.

I wonder whether the more physical lifestyles (farming, more manual labor, more physical housework) increasing testosterone levels played a part too in making folks look older/bigger.

I keep noticing this, and then keep reminding myself that it's cliche for seniors like me to see adults as kids. But then I watch, say, an episode of Dragnet, and the feeling comes back. Jack Webb was 35 in 1955, in that show's prime. He looks normal for the times, but so much older, or perhaps mature is a better word, than a modern 35 year old. Multiply this observation by a large number of cases.

You could test the theory with photos of class graduations and reunions for various years, with faces extracted, normalized and pasted into a standard setting. I'd bet it's real.

I can tell you this - most of my peers from HS that went on to work in physically demanding (often outdoors) jobs look around 10 years older than the average, while the ones that got cushy / low-stress indoors jobs still could go for late 20s / early 30s (I'm in my mid 30s).

My bet is on environment, stress, and genetics.

But those that by far aged the most, were the girls that would spend their teens and probably entire 20s in the tanning bed. Probably guys, too, but we didn't really have many dudes that focused on that.

I'm surprised no one has brought up smoking and drinking yet, as per capita more people were heavier drinkers and everyone smoked. Also, you don't have to go back very far in history and more people were working industrial jobs that were physically hard. Even those people you would have seen on TV in the 70s (for example) would have been more statically likely to have had a childhood on the farm than anyone you see in the public eye today. As a kid I was always outside playing, even in winter. Today kids spend far less time outside plus we are more aware of the need to protect our skin.

As far as my own experiences go, it mostly comes down to fat. That slight (or less slight, for many) fattiness in the face evokes a sense of softness that we seem to interpret as younger. If this is offset by decent skincare and less sun wrinkles, it makes people seem a little younger than their sharp-featured peers. When you add in some of the cultural aspects of overall appearance and behavior, it gets even stranger: have you ever noticed how someone who usually wears t-shirts and jeans/shorts tends to look awkward in even a well-fitted suit? The way we carry ourselves sends a huge amount of signal about confidence which also tends to come from life experience (inb4 "source?", I'm not going to provide sources, look it up yourselves if you dare).