Why not let it be natural. I'm 62 and my hair is light red. I don't do any thing to it nor do I intend to. As time goes by it will probably get a dirty sandy color. That's what my dad's did long befor going gray at 80.
I have noticed that very few of the old men have their hair to be completely white...which looks good no doubt...but it neither makes any difference if one old doesnt have white but a mixture of balck and white hair.