I would say the dividing line is when you have lost your street smarts, you can't prevent people from manipulating you, when you can't answer the 3AM emergency

I would say the dividing line is when you have lost your street smarts, you can't prevent people from manipulating you, when you can't answer the 3AM emergency from the JCS. That being said, the line is different for everyone, and your declining abilities make it difficult to recognize in yourself. THAT being said, a large part of the job is just to sign things or not sign things that the staff has set up. That can be done as long as there is still a heartbeat. Without naming names, there was one president I'll call GWB who definitely was the alpha male in the room and not in decline but was easily manipulated. Another I'll call RR who went senile in office. That's why we have elections. If someone else decided how old was too old, they would be in charge, not the president.