I don't know, but I find this pattern attractive on both men and women, personally, too.
Why does anybody like anything?
I've known so many people to have widely diverse tastes in what they find attractive, I just cannot buy the whole "blah blah because fertility because breeding blah" that we get constantly from some folks. I'd be more inclined to believe that as children growing up, we observed something that imprinted upon us. We might not even become aware of it until much later in life. I realized somewhere along the line that I find older men and women attractive because it was not my parents, but my grandparents, great grandmother, and great aunt who put the most and best into raising me. My parents meanwhile were moody, busy, stressed, distracted, uninterested in me, and sometimes unpredictably ragey. And I didn't get along with other children. So it only makes sense that I find older people to be more genuine, wise, and form trusting and loving relationships with them, and I find them attractive. Some of them anyhow.
My boyfriend is rocking the silver at the temples of his dark brown hair, at 60 years old, and it looks great. I'm starting to get some silver too, at 40, but I think I'll end up with a streak of it. I have long, dark brown hair that I part in the middle, with no bangs. Hippie hairstyle. And it looks like a streak about 2" wide is forming in the middle of the on the left side. I think it's cool.