A few guys look fine with grey in their hair, but not me. I keep it out. Just don't go too dark, it isn't a good look. Lighter brown is good - with a couple of red highlights, as if the sun did it. The Just 4 Men product is great - takes a couple of minutes every couple of weeks, costs less than $10.00. Not a problem, and if you don't go too dark or all one color, it will not be something that others can spot as a "dye job". Look at my hair in my main photo. I do my own color and it looks 100% natural - even up close. Get advice on how to do it right, or just let the guy or woman where you get it cut do the treatment. It just looks infinitely better IMO to have natural, healthy color up there instead of the plain old gun metal grey. I can be grey in my 70s, I sure don't need to be letting that happen in my 30s.
I have seen guys passed over for promotion in favor of a younger guy. The sub-conscious thought is that the younger guy will bring newer or more advanced / up to date training or experience. The younger guy is thought of as more with it - even in medicine. No way am I getting passed over (at 37) for some hot shot fresh out of his residency in his late 20s or early 30s because I look tired out or past my prime.