Their chronological age is irrelevant because God can and will see to it that they have all the energy they need to fulfill their God ordained roles. Besides that the Beast is empowered by Satan. If you were aware of the power of God, you'd know JFK's chronological age is irrelevant. Same for Kissinger.
Really same for all of us. Our chronological age is insignificant. Jesus can and will rejuvenate, transfigure, transform and empower a lot of old people. For Jesus, just as easy as healing.
Certainly the man JFK had but one literal head. And when he publicly reappears he will have but one literal head. He won't reappear as a literal "beast" either. He'll reappear as a literal man. And the world will be amazed to see him .... because like you, the world is persuaded he is dead and gone.
You say JFK only has one head that was wounded to death, but that is not what the scriptures say.
Revelation 13:3 And I saw one of his heads (as in plural) as it were wounded to death; and his deadly wound was healed: and all the world wondered after the beast.
So, are you going to believe your theory or are you going to believe what is already written!!!