Its very rare that a Heavyweight beats a 'great' in their prime

[Trainer Monkey]

How can Ali be past it,when he beats Foreman a year after Frazier beat him?
And how can Frazier be past it when Ali beats him a year after the Frazier fight?

Sorry, say that again

Just edited
If Foreman/Frazier was two greats in their prime
Ali beats Foreman 1 year after Frazier/Ali 1
So Frazier/Ali 1 would logically be two greats in their prime
And if Foreman/Frazier was two greats in their prime
Ali/Frazier 2 happened a year after it