-_- their teeth would have rotted from overuse, since humans typically only have two sets (if you count 12 year molars and wisdom teeth as part of the adult set). Even with modern dental care, toothpaste, etc, and if the teeth of those past humans were twice as durable as our modern ones, they wouldn't last a 400+ year lifespan. Furthermore, people in the past tended to have more rough plant matter and even bones in their diets, which wears down teeth even faster. If one asserts that their teeth were durable enough to withstand those lifespans, then the wear on their teeth would not be reflective of their age.