Dry mouth is not a normal part of aging. Causes include some medicines, radiation therapy, chemotherapy, and nerve damage. Salivary gland diseases, Sjogren's syndrome, HIV/AIDS, and diabetes can also cause dry mouth.
Treatment depends on the cause. Things you can do include sipping water, avoiding drinks with caffeine, tobacco, and alcohol, and chewing sugarless gum or sucking on sugarless hard candy.