Yes once past 70 ( our alloted time scale on the best of authorities ) we expect the advent of progressive senility. The actual time scale depending on personal genetics and state of health but what we are getting now is a veritable plague - an abnormal plague!
May I suggest a simple cause - mercury amalgam dental fillings.
The whole matter is a nonsense of course Dentists know damn well that mercury is a dangerous nerve poison. But it is easy to use and the leakage associated with it ( as adjacent dentine cells die off ) guarantees frequent and profitable return visits, until there is no longer any tooth left to drill and then, depending on income, it is either dentures or implants ( very profitable! )
The solution is to ban mercury amalgam and replace existing mercury fillings with composite...