Teeth lasts for ever. If gum condition is good teeth will b seen till death of an individual. Even after death and burial teeth do not undergo disintegration.

Well the answer for your question can be just hypothetical just like your question..it just lyk asking the approx life span of a person. Well only brushing is not the super power which will save your teeth. There are multiple reasons which effect the life span of a tooth. So if you want your tooth to get retired as late as possible please visit a dentist as early as possible. All the best