If your on a diet, how many grams of sugar should your intakebe?

Very little. If you're dieting, it's best to avoid pure, and processed sugar. If you're asking about the total amount of carbohydrates (starch, sugar, fruits, and vegetables), it's best to keep it below 60 grams at the age of 75 and get those carbohydrates from complex, whole grains or low sugar fruits & vegetables and avoid processed sugar (candy, cookies, soda white bread, bagels, etc.) as much as possible.