I'll restate the most pertinent facts:
In the last half-century, the average age of major championship winners is 32.
75% of majors in that period of time have been won by players under 35 years of age.
Less than 1% have been won by golfers over 40, and less than 6% by golfers over 35.
That's a lot of data, and those numbers indicate, at least to me, that top-level golfers age at pretty close to the same rate as athletes in other sports. (Again, the curve that most resembles that of pro golfers is MLB pitchers.)
You can think whatever you wish about the age-old question of golf as a game vs. a sport, and I'd be the first to admit that it is possible to play golf at a higher level longer than most other sports; certainly longer than either collision sports like football or highly aerobic sports like basketball. But those are matters of degree, not indications that golf is fundamentally different at the highest levels vis-a-vis that aging process.
So to return to the original question that Tom posed in post #170, the overwhelming likelihood is that neither Day nor McIlroy will be winning major championships in their early 40's. If they aren't, it won't be because of their swings or their workout habits or anything else more complicated than the simple fact that they got old.
Overwhelming? Of the top 44 majors winners, 25 won majors after age 35. 15 won majors after age 40. (Source: Wikipedia, plus my counting.) Those golfers you noted earlier, who stopped winning by their mid-30s, are the exception, not the rule.
I think you're not quite using the stats correctly in that last post. The % of events won by golfers overall says nothing about the odds of any specific golfer to win. And the numbers show that golfers who win majors (multiple) in their 20s and/or early 30s are a good bet to win later. Over 50% have won after age 35; and over 33% have over 40.
No huge surprise. They proved they have what it takes, mentally and physically. And because golf is so un-athletic, they carry those abilities with them, longer than any athletic sport I know of.
Jim,
I'll accept and agree 100% with the idea that golfers who win early are more likely to win later, too. This is true in every sport, I think; the better a given athlete is at 20, the longer they tend to be good. MLB teams draft hard throwers coming out of HS because those pitchers tend to have more room to decline and still pitch effectively vs. the guy who throws off-speed stuff; when the slower thrower declines, he's throwing BP.
I'm going to disagree with you, though, about what the overall stats tell us about the odds for an individual. If 76% of majors over the last 50 years have been won by players 35 and younger, and only 8% by golfers 41 and older, I think you can look at any player in their 20's and say that their window for winning begins to close in their mid-30's, and is very close to, if not completely closed by the age of 40. So if you look at Speith, McIlroy, Day, Fowler, DJ, or any of the other of the young guys that are so impressive right now, and try to project their career path, the wise bet would be that none of them will win a major after the age of 40, and maybe not even after the age of 35. If one of them does, that doesn't change the overall picture very much; it turns them into an outlier like Nicklaus and Boros. The odds are still going to be the odds.
I also have to disagree with you about golf being "so un-athletic", though we'll NEVER settle that debate. For sure, it isn't aerobic, for sure it isn't about brute strength, or quickness, or lateral movement, or vertical leap, or a bunch of other stuff that the NFL combine tests. But at the Tour level, there is a lot of athleticism in what those guys do. And that WILL decay with age, beginning in the mid-30's; swing speed will decline, hand-eye coordination will decline, strength that enables one to maintain spine angles will decline, and so on. The margins at that level are just tiny, and it doesn't take very much decay at all for a given player to no longer be in contention for winning. Nobody gets a pass from Father Time, including pro golfers, which is why winning majors hugely favors those below 35. It just does.
So to return to Tom Doak's restatement of the original question in the thread, I agree that it is unlikely that Day or McIlroy will be winning majors at the age of 40; it's far more likely that they won't even be in contention regularly by that age. But it won't be because they train hard and swing hard NOW; it'll be because that's the way top level sports work for MOST people that God has touched and given the ability to be transcendent at some athletic endeavor. They'll just get old.