When I was in my early twenties I was very overweight and didn't exercise much. I had tons of acne and looked much older than I do today! The past decade I have been mostly vegetarian and it has made me look much more youthful (matter of my opinion and others that tell me too).
When I stray from vegetarian and an active lifestyle I see the years on my skin mostly. But, whenever I'm consistently vegan/vegetarian with moderate daily activities.... I look and feel young!
So, I don't know if that offers much evidence, but I would say- for me- the way to stay youthful in looks and emotions, eat right (nothing processed) and exercise daily!
My two cents.