I'm 54, and started getting gray hairs when I was 7! I decided long ago that I was NOT going to color my hair.
Reasons:
1) Cost - I don't want to keep paying for hair color.
2) Chemicals in the color - my mom is highly allergic to them, and I'm a clone of my mother, so I don't want to take the chance.
3) Lazy! I can't be bothered spending time coloring my hair. I have WAY more important things to do with my life.
There are probably more reasons, but that's enough, right there.