Your teeth and gums age as you do. Even if you take excellent care of your teeth, just by chewing and cleaning will wear them down over time. Faster if you clench or grind your teeth. As you age your teeth can start to look darker due to aging dentin.
Older people may have more plaque buildup on their teeth. Though this is not necessary due to their age then age related physical changes that can make basic dental care like brushing and flossing their teeth harder to do. (Such as people who may have arthritis)
Not only are your teeth aging but your gums age too. Gums will naturally start to recede over time. If your gums recede to where the roots of your teeth are exposed your teeth may become sensitive. As you age your dentist may advise that you to see them more often in order to maintain good preventive health care.