Why do our toenails get ugly as we age??

Just another thing that gets out of control as we age, I guess. I have been in socks and closed-in shoes all winter and got out some sandals a few days ago and prepared to give myself a pedi. What is going on with our toenails as we age? Not to be graphic, but the big nails appear to be turning yellow and they are much more brittle to cut than they used to be. The other toenails appear to be getting thicker and harder to trim. I have a friend who is a podiatrists, and I know that his office is a revolving door of older patients for toenail trims. I suppose a lot of that could be because they can't really get down there to trim them, but I am just talking about the issues that I mentioned.

Well, at least I covered my disgusting looking nails with a pretty pink polish so I won't have to offend myself. Some days I hate this aging thing.