Yeah, I hear you. I do wonder how long Roger might have played without Djokodal. First of all, he very well could have won at least one Calendar Slam in 2006-07. If he had, and then dominated for a few more years in 2008-12ish, he might have been ready to wind down. I mean, who would his main competitor have been, Andy Murray?
In other words, he might have won more in 2008-10ish, but I'm not sure if he would have still been playing after around 2015.
People make a lot about improvements in medical tech and fitness, but there has to be the will behind it - and clearly Roger was "inspired" by Djokodal. Agassi already played longer than the greats of the 80s and 90s, winning his last Slam at 32, his last Masters at 34, remaining in the top 10 at 35 and only retiring a year later. I think that was partially him making up for a mispent youth. Agassi's path echoed Connors somewhat, though he retired more quickly after falling from elite status, while Connors lingered. Roger, then Rafa and Novak, essentially added +5 more years to what a tennis career looks like.
It isn't entirely a new precedent, except as far as the Open Era is concerned. Laver and Rosewall were still great into their 30s, and Rosewall played until he was almost 46. And of course Pancho Gonzales was still a very good player in his 40s, wining two Masters equivalents at 41 years old. But starting in the md-70s or so, the game got younger - the power game of Connors and Borg. Stan Smith and Ilie Nastase declined from their peak level in their late 20s. Newcombe and Ashe were a bit more of holdouts from the Laver era, and were still good in their early 30s, but retired shortly after. Connors was a bit of an outlier and considered on the old side when he won his last Slam in 1983 at 31. Since then, and before the Big Three, or 1984-2011 before Federer entered his 30s, only Agassi and Sampras were older Slam winners, and just barely.
Consider how many Slams the Big Three won at older ages than Connors' last: Federer with 3, Nadal with 7, Djokovic with 12. Plus, Stan's last in 2016. They re-wrote the possible, or at least the norm of 1970ish to 2010ish.
Here's a crazy stat: Novak won as many Slams as Edberg and Becker combined at an age older than Jimmy Connors' last Slam.
We won't know for some years if this longer prime will translate to younger generations. We might get some glimmer of it in the next few years, as Next Gen enters and goes deeper into their 30s. Medvedev has already declined somewhat, and who knows how long Zverev's candle will burn. Rublev and Fritz seem to be trending downward, and of course Tsitsipas is a shadow of his former self. These guys are all 28-30ish. So we're really looking at 2031 and beyond, when Jannik Sinner turns 30.
See, you got me going.