We have better medicine, better food and diet, better living conditions (more white collar vs. blue collar jobs, better life balance vs. all work no play, etc.)
It isn't perfect, but my life is significantly less difficult and stressful than my father's or grandfather's life.
I've noticed that men who work hard jobs often look older than they are. They're often taking physical injuries, and may be outdoors in the sun without UV protection. They end up stooped over, wrinkled, asymmetrical, much sooner than people who aren't exposed to those kinds of conditions.
And from what I can tell, the average person's working life before the mid-20th century, roughly, was comparable to today being a roofer, landscaper, warehouser, on-foot postal worker, something like that, in terms of physical wear on the body. But maybe worse.
We have far more processed garbage, more pesticides, more chemicals in general. I don't think it's so cut and dry in the nutrition department.
I suspect it was mostly just people smoked a lot. I remember the 80s, I remember everywhere public except hospitals allowing smoking indoors still. It was a huge portion of the population that smoked, at least back in IL where I grew up. And it was often discussed about, how unhealthy certain relatives/friends were and how fast they were declining visibly for their age. There was usually an element of addiction like smoking over a pack a day implicated.
Also back when I was a kid, everyone was putting on sun-tan lotion in the summer. We didn't even have sunscreen in our home. What we had instead was Solarcaine to numb the pain of sunburn. My dad worked as a concrete construction worker and by the time he retired his skin was so utterly wrecked. I don't think he ever put on sunscreen once in his life, too macho for that.
Living in constant stress, fear and potentially malnutrition and disease takes a pretty big toll on you. 20-somethings begin to look like 35-40 year old men really quick.