I am 42 and began eating Paleo a year ago. About 6 months ago, I noticed that the gray hairs I was pulling out with tweezers all the time were not growing in anymore. My hair was also healthier than it ever had been.
Then, in October, I was under quite a bit of stress and my diet suffered. I was eating wheat almost everyday. I caught a cold, and because I didn't feel well, I didn't have the energy to cook or shop for my regular Paleo groceries. I kept buying prepared foods or going to the deli for a sandwich. Not only did I keep getting sicker, but guess what? Some gray hair started appearing again. My skin also broke out - something I hadn't seen in 10 months.
As soon as I felt well enough I stopped all the nonsense and got back to my Paleo way of eating. I made rest and exercise a priority. My hair is healthy and shiny again and no sign of any new gray!
I remember hearing that you can tell how healthy a dog is by its coat of fur. If that is true, perhaps people are the same way!