I do not appreciate Roger Federer as much as the generic tennis fan should.

I know for certain that I rooted against him throughout the Aughties, mostly because I was sick of him winning everything — which is pretty much what he did for years at a time, back then.

From 2004 through 2007 Federer won 11 of the 16 Grand Slam events, finishing second in two more.

He also played a leading role in exploding what had become the quaint American expectation that one of its native sons would win a major tennis tournament every year — and sometimes more than one.

It was pretty much all Roger who turned Andy Roddick into a big-hitting also-ran, defeating him in four slam finals, from 2004 to 2009, including three Wimbledons, punctuated by the crushing 2009 final that ended 16-14 to Federer in the fifth set and maybe broke Roddick’s spirit.

That result also broke a record for “most major championships, 14”, which previously had been held by another American, Pete Sampras.

It was Federer, too, who did not see the romance of a battered Andre Agassi reaching the 2005 U.S. Open final, beating him and pretty much ending his career.

But I have come around a bit on Roger. I know; it’s quite generous of me.

I was watching today when he dismissed Marin Cilic to win the Australian Open and secure his 20th major championship.

It went five sets, but it never felt that close, especially at the end, when Cilic melted in a fifth set that finished 6-1.

I think even American tennis chauvinists can be OK with Federer winning 20 majors. It is a tribute to his continued skill at what used to be advanced old age (36) in the game.

It also says something about how he takes care of himself, and prepares and how his style — all smoothness and precision — allowed him to win in Oz at least in part because he was the last man standing of the thirtysomethings who collectively have dominated the game for most of this decade.

–Top-ranked Rafael Nadal, 31, retired in the fifth set of the Oz quarterfinals with a hip injury.

–Novak Djokovic, 30, still dealing with an elbow injury, went out in the fourth round to the Korean Chung Hyeon — who later retired against Federer in the semifinals.

–Andy Murray, 30, had hip surgery earlier this month and did not play the Australian Open.

Woody Allen apparently said, 40 years ago, that “Showing up is 80 percent of life.”

Federer showed up in Melbourne, and the other three guys with whom he has shared 47 of the past 52 major singles championships were not healthy enough to get to the final … and, well, there Roger was in the championship match against a middling player.

As well as studying Federer’s game, someone may want to talk to him about his fitness regime. He not only failed to go away, during that nearly five-year gap between major titles (2012-17), he now clearly is the healthiest of the foursome and has won three of the past five majors.

Peak Federer, in the previous decade, was just better than everyone else — aside from Nadal on clay.

Now, he seems to be the one man most likely to be able to get on a court and produce an effort that looks quite a bit like what he might have done a decade before.

Not all of that is genes or luck. Can’t be. As one of the TV guys said, “Time waits for no man except Roger Federer.

We have to give credit to the tennis star who has achieved the best approximation of his former self over the past 13 months. That man is Roger Federer, and now that he doesn’t have to worry much (if at all) about facing an American in the final … well, he’s a lot easier to for me to like, as well as admire.