Well, I did take that into account, which is why I would consider those stand-out performances at least for their age.
But at the same time it's not like we don't know what these guys are capable of and would blow us away with a performance in their 30s that would put their 20s to shame, like they played at 60-70% of their potential earlier.
The point is that you lose something with age, physically, but you can make the best out of it by cutting errors, working on improving whatever you can, which is why AO 19 and RG 17-20 are performances that deserve appreciation.
You can see for instance that Nadal at 34 looks like a bull on his feet, can sprint laterally hard, can punch a ball, but his younger self was a cheetah, so light on his feet and so quick changing directions. That's physical decline.
That was so noticeable if you watch their 2007/2008 semi and then 2013 semi. How Nadal's both movement and hitting patterns changed with age and certain playing patterns started actually cracking his game, quick changes of directions into his BH, testing his balance, or deep CC backhands drawing short responses from his FH.
2020 has 7 more years of decline and all these issues would be exacerbated as there is no way to alleviate them, but facing 2020 Djokovic, whose weight of shot was nothing like his prime self would never expose that.
As for 2019 Djoko, he had a lighter frame, so less punching power than his younger self (except 2015-2016) and this on an older body, so naturally less explosive.
His balance and counterpunching were still exceptional, but his weight of shot and ability to redirect heavy hitting were not tested whatsoever.
So in short both guys got the perfect opponents to highlight their current strengths and hide their weaknesses and AO 2019 Nadal in particular was like watching prime Big 3 play Ferrer, was getting subjugated in all aspects of the game.
Djoko tried to outhit Nadal in very slow conditions and got exposed by the guy with cleaner clay movement and more weight behind his shots.
And sorry if the long posts are hard to follow