For all of those people that think winning is easy at an old age, we'll get to see what Nadal and Djokovic do during their age 33-37 years. And the good news is that they won't have to face an ATG during his absolute peak. So they will have a huge advantage over old Federer.
Here's the bar that Federer has set for old players. And he did this going against Nadal and Djokovic that were 5-6 years younger than him.
So far, from 2014-2018, Federer(age 33-37 seasons) has gone:
223-36, .861 overall
49-18, .731 vs the top 10,
made 10 slam semis, 6 slam finals, and won 3 slam titles
If Nadal from 2019-2023(age 33-37 seasons) and Djokovic from 2020-2024(age 33-37 seasons) can put up the same results despite not facing 2 ATG that are 5-6 years younger, then I'll start to believe that age isn't as big of a deal as I originally thought.
Fed's incredible play as an old man is what puts him at the top. Federer is a combination of young Borg and old Rosewall wrapped into one career. It seems impossible.
Let's see Nadal and Djokovic age nearly as well as Federer. Time will tell. But I would bet a lot of money that they won't. They will someday appreciate how tough it is to win at an old age. Luckily for them, they aren't that old yet. But both have clearly experienced a dip in play.