That's a ridiculous fact you mean.
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Look at the number of wins for Djokovic coming after 29 which was previously thought about the time in which there is a massive drop off in performance.
Given like you have pointed out the age difference between him and Nadal is only a year why didn't the 'GOAT' in your opinion win more slams at what would have been his prime 25-28?
Overall Djokovic has had less injuries, married with a lack of younger players who were any good to challenge him. That one sustained spell where Djokovic was injured helped Federer and Nadal increase their stash late in their careers.
He was not as good as the others in around their prime years but he has maintained a level that the others could not. As I said, outlasted.