I started going gray in my mid-thirties, and I have to admit that the first few years I used some of that "Just for Men" beard coloring. This had less to do with me wishing to avoid looking my age than the fact that my gray hair tends to come in distinct splotches as opposed to a balanced salt-and-pepper look.
Still, this was vanity, and this could be interpreted as a cardinal sin, should I be so judged in the hereafter.
These days I let the gray appear where it may, and I view the acquisition of gray hair as I would badges of honor. I should add that I work in a field (academia) where gray hair is not necessarily seen as a detriment, and in some cases being gray- or white-haired might be viewed as a sign of scholarly authenticity.
Or doddering senility, but that is another story.
Yet for much of the world - especially the youth-obsessed business world - gray and/or thinning hair increasingly means personal irrelevance, declining energy, and outmoded thinking. The problem is even more acute for women, as women face significant stigma by having gray hair. Many folks will spend thousands of dollars fighting the natural and inevitable changes to their hair, and with good reason: there is a perception that having gray hair is equivalent to career suicide.
Perhaps in the next few decades gray will become more fashionable, especially as the American population continues to age. We may also see the pendulum swing back to respect for the wisdom that our elders have acquired, instead of our absurd obsession with the cult of juvenescence.
Anyways, I hope to live long enough to be relevant for another four decades. Provided I do not succumb to Alzheimer's disease or some equally destructive condition, I plan to write and teach as long as my body permits.