Most of the population above age 50 might have some form of voice problem which can be supported by following a few simple rules. There is a lot of natural variation in how the human voice sounds. But once your voice prevents you from communicating properly you may have a problem. Parkinson's disease, for instance, makes the voice soft and mumbled and people might find it hard to understand you.
Other times you may be misusing your voice without realizing it. Researchers at the University of Arizona are currently looking into 'vocal hygiene' and have some useful suggestions to offer. People who use their voices professionally such as singers, auctioneers and drill sergeants are often advised to rest their voices if they develop nodules on the vocal cords from over-use. The Arizona researchers feel it would be better if such people learned to use their voices more carefully.
You should never shout or yell. If you have to make yourself heard above background noise, it is best to use a microphone. It is also important to hydrate your vocal cords, and for this you should really be aiming for a dozen eight ounce glasses of water a day. Caffeine in coffee tends to dehydrate the vocal cords so, if you have a concern about your voice, don't drink more than a couple of cups a day. Smoking is a major irritant to the voice (you can often hear this when a heavy smoker talks), so if you value your voice, you need to quit tobacco.