Here's some science behind that concept:
I started playing catch-up with some Robb Wolf podcasts recently and stumbled on this one. Wow. What a keeper.
Dr. Michael Rose's research, which he describes at length in the podcast, has led to the conclusion that aging represents a cessation of adaptation. Translated, from a dietary perspective: at a certain age, our bodies cease to be able to handle certain neolithic foods as well as we previously have.
So, while no one should be eating crappy processed Frankenfood at any age, younger folks can do fine, even thrive, on a wide-ranging diet that is not remotely paleolithic. However, at a certain point -- Rose says between 30 and 50 years old for most people -- the ability to handle that neolithic food load decreases sharply.
In other words, between ages 30 and 50, the *adaptation* to neolithic foods disappears and those foods become a significant source of inflammation and aging. His prescription: eat paleo as you get older than 30, and certainly by age 50.
The concept makes sense to me. I watch 20-something friends shovel in all sorts of things that I wouldn't eat now, and they do so without significant current consequence. When I ate those things in my thirties and early forties, I got heavier, softer, less-athletic, and generally less healthy. When I went paleo in 2010 at age 46, things changed quickly for the better. I leaned out, gained energy, and generally felt stronger and more alive.
You probably knew the basic idea already: when you get to a certain age, you cannot eff around with bad food and drink like you used to. Dr. Rose's research provides a strong genetic/evolutionary-science basis for that "obvious" fact.
Link to the podcast is here.