Just as there’s a lower age limit on when someone can become President, so too should there be an upper limit. The same should go for Congress as well. And when a President or Congressman reaches that age limit, they should be forced to retire at the end of their current term, even if they are otherwise still eligible to run for another term.
What should that upper limit be? It’s hard to say, but generally speaking I think it goes without saying that anyone in their 70s or above simply does not still possess the mental acuity that these jobs require.
Case in point, the current occupant of 1600 Pennsylvania Avenue as well as several members of the Legislative body.