Not taking care of your feet. I have regularly seen older patients come into the hospital with very long toenails and nail fungus that HAS to be a 20-year (at least) case. I know the older folks are often on a fixed income, but Medicare pays for a podiatrist to do nail trims. This is not a luxury. If you can't reach your feet, see a podiatrist regularly. There are treatments that work. As we age, often the blood vessels in our legs aren't optimal, so it's important to address issues early. Ingrown toenails and fungus can present - or indicate - other problems.