he was 40
not much weaker . technically the same age as oden if not older .
when you read current kaido take on the 9 scabbards
and they cant even open up an old scar.
you see zoro put all he had into an attack possibly imbuing coc into it to replicate something oden did casually
when you see zoro struggling to tame enma recognizing the level oden had to be at to wield this thing
I think you will begin to understand why 20 yrs later kaido still holds oden in high regard.