Haelfix, glad to see you around. I feel your pain. I have written extensively on this topic, so will almost certainly repeat myself, but I've also done a fair amount of research so maybe what I've found is worth saying again. (Forgive me for this being so long...it is a fascinating topic and you got me excited about writing about it...I should probably turn this into a blog).
The big question seems to be: Are players peaking later, both in terms of when they start peaking and how long their prime years last, or are the older players staying in charge of the tour because of a weak generation of younger players? While it is hard to say, I think the best answer is: some of both.
For instance, it is unarguable that we are seeing three of the greatest players of all time in Federer, Nadal, and Djokovic. Their dominance as a group - winning 44 of the last 55 Slams (80%) - is probably unparalleled as a small group, at least since Laver and Rosewall on the pro tour in the 60s; for the sake of comparison, Connors, Borg, and McEnroe won 26 of 44 Slams (59%) from 1974-84.
You may be familiar with my "generation theory," which is a handy way to look at different cohorts of players. I prefer to use the ranges beginning with birth years ending 4 and 8, because I think it more accurately groups peers than 5 and 0. So Roger is in the 1979-83 generation, Rafa and Novak are in the 1984-88 group; we can see that Cilic and Del Potro, the youngest Slam winners on tour. As you point out, these guys are now 28 and are the youngest players with either a Slam or Masters title - which is truly unprecedented in tennis history.
Now take a look at the ages of all year-end ATP #1s going back to 1973: 27, 22, 23, 24, 25, 26, 23, 24, 22, 23, 24, 25, 25, 26, 27, 24, 29, 24, 25, 22, 22, 23, 24, 25, 26, 27, 29, 24, 20, 21, 21, 23, 24, 25, 26, 22, 28, 24, 24, 25, 27, 27, 28, 29.
OK, sorry for putting you through that. The first thing that stands out is that they were all in their 20s. Now there have been players who were #1 in their 30s, although a rather short list: Jimmy Connors, Ivan Lendl, Andre Agassi, Roger Federer, and soon-to-be Andy Murray. Yes, Andy Murray will be the fifth player to 30 years old and #1. Who would have thought?
But let's look further at the numbers. Broken down by age, here is the number of times year-end #1 was accomplished by different ages:
20: 1
21: 2
22: 5
23: 5
24: 10
25: 7
26: 4
27: 5
28: 2
29: 3
Now as you can see, it expands at age 22 then spikes and peaks at age 24, with 25 having the second most, and then decline. We can also look at age 22-27 as the "plateau" of #1 players, with 36 of 44 years (82%) being within that range.
So what about generations? How do they represent?
1944-48: 1 (Nastase)
1949-53: 5 (Connors x5)
1954-58: 2 (Borg x2)
1959-63: 8 (McEnroe x4, Lendl x4)
1964-68: 3 (Wilander, Edberg x2)
1969-73: 8 (Courier, Agassi, Sampras x6)
1974-78: 1 (Kuerten)
1979-83: 8 (Hewitt x2, Roddick, Federer x5)
1984-88: 8 (Nadal x3, Djokovic x4, Murray)
1989-93: 0
1994-98: 0
A few really interesting things to look at. First of all, you can see which generations were strongest, with four having 8 years at #1 (and the 84-88 one with a great chance of making that 9, even 10). But most importantly, the 89-93 generation has not (yet?) had a year-end #1, and thus is the only generation of the ATP era to not do so. Or is it?
It is well known that the 74-78 generation is relatively weak, but also sandwiched between one of the strongest generations (69-73) and Roger's group which, if you include Roger, is also a strong generation (Weak Era Theory aside; actually, that's the main problem with WET - it looks at the generation without Roger. Take away the best player of any generation and it will look substantially weaker; you can't exclude Roger, because he is part of his generation...but I digress). Another very weak generation is the 1939-43 group, with only three Slam winners and one (Arthur Ashe) multi-Slam winner. That generation came on the heels of the most dominant generation in all of tennis history: the 1934-38 group which included Rod Laver, Ken Rosewall, Roy Emerson, Lew Hoad, Manuel Santana, Ashley Cooper, and several other Slam winners.
We don't have ATP rankings from before 1973, but TennisBase.com has their own ranking system, and we can look at who they have as the #1 in the early years of the Open Era, at least: Rod Laver in 1968-71, and then Stan Smith (44-48) in 1972. Before the Open Era it is all Laver, Rosewall, and Pancho Gonzales going back to 1954, so Ashe's group was never #1. That said, both the sportswriters and TennisBase gives him #1 in 1975, and TB also disagrees in a couple other years in the 70s, giving the #1 to Vilas in 1977 and Borg in '78, so Jimmy Connors was only #1 according to that site's deeper statistical reading twice rather than his ATP five times (although Jimmy does get one back later from McEnroe in 1982).
What about Slam titles? Well, if we look at all generations which won at least one Slam in the Open Era, we start with 1934-38.
1934-38: 10 in the Open Era, tons before
1939-43: 3 in the Open Era, 2 before
1944-48: 12 in the Open Era, 3 before
1949-53: 15 in the Open Era
1954-58: 16
1959-63: 17
1964-68: 23
1969-73: 33
1974-78: 9
1979-83: 24
1984-88: 34
1989-93: 0
That "zero" is rather striking, especially considering that this group is no longer young - all players are at least 23 years old, and some are turning 28 years old this year. It is also interesting to note how you have weak generations squeezed between stronger generations. But even the previous weak generations--39-43 and 74-78--found ways to win Slams. If we look only at the 74-78 group, we have Kafelnikov (2), Kuerten (3), as well as single-Slam winners Moya, Costa, Gaudio, and Johansson. But consider this: These guys played during a time when the courts were less homogenized, and there was no clear "King of Clay" - but rather a group of "lesser kings" (dukes?). Of their 9 Slams, 7 were at the French Open.
Actually, this might give the next generation some hope. Nadal hasn't won the French Open since 2014 and Novak's struggles seem to be continuing. Even if Rafa comes back and wins it this year, it may be up for grabs again in 2018. With Dominic Thiem born in 1993, he might be this generation's best chance of winning a Slam.
Don't get me wrong: I think players of this generation will win Slams, although the clock is ticking. And it will almost certainly be far less than the 74-78 group (9) and probably even less than the 1939-43 group (5). As of this writing, I think the players of the 89-93 generation with the best chance of winning a Slam are, in order: Dominic Thiem, Grigor Dimitrov, Milos Raonic, Kei Nishikori, and then...Pablo Carreno Busta? Who knows, maybe he'll sneak one in at Roland Garros. Jack Sock? David Goffin? It is hard to imagine. But regardless, I do think we'll end up seeing 2 or 3 Slams won by this generation, maybe 4 or 5.
All of which is a long-winded way of telling us what we already know: That the 1989-93 generation is historically weak; certainly it is the weakest since the 1939-43 group, far weaker than even the relatively weak 1974-78 group. But the 1984-88 group is also historically strong, certainly up there with the 68-73 group as the strongest of the Open Era, although neither quite compares--in terms of era dominance--to the 1934-38 group. But here's the point: A strong generation looks even stronger with a weak younger generation, and a weak younger generation looks even weaker with a strong older generation. So both are exaggerated by the extremes of the other.
As I've written elsewhere, there's reason to hope. The 1994-98 generation looks far more promising than the 89-93 group, especially once we get to players born in 1997. If we tag on Thiem's 1993, we have some talented players to look out for:
1993: Thiem
1994: Pouille
1995: Kyrgios, Edmund
1996: Coric, Khachanov, Medvedev, Chung
1997: Zverev, Fritz, Rublev, Opelka, Paul
1998: Ruud, Tiafoe, Kozlov, Lee, Mmoh, M Ymer, Tsitsipas
1999: De Minaur, Shapovalov
2000: Aliassime
There are others, but those are the guys I think bear especial watching, with a decent chance of at least becoming a top 20 type. At least a few of those guys will win Slams and be #1.
OK, done for now.
