What causes cavaties in your 50s?

Acid: Acid from the bacteria that reside in your mouth causes cavities. This can occur from infancy (baby bottle syndrome) into later adulthood. I do not know your dental history, eating habits, or hygiene habits, so commenting on your situation is difficult. Have your dentist explain what is causing your condition.

Not age dependent: The same thing that causes cavities in your 40's, 30's, 20's, etc. And also will in your 60's, 70's and beyond. The answer is poor oral hygiene, not brushing and flossing properly after meals and snacks, and foods and liquids that are high in sugar and carbohydrates that stick on teeth and promote tooth decay. If you're suddenly getting cavities, something has changed. Figure out what.