John McEnroe turned 60 this year.

Wearing his Mets ballcap in the Player’s Garden as the rain fell in Flushing Meadows, McEnroe said to a 60th-birthday well-wisher: “Don’t rub it in.’’

In fact, 2019 marks a bunch of McEnroe milestones. It’s 40 years since McEnroe won his first U.S. Open. It’s 35 years since his magical 1984 season, when he won Wimbledon, the Open and nearly captured his only French Open.

It’s also 35 years since McEnroe won his last Grand Slam title. Who could have imagined after the 25-year-old lefty genius took his fourth Open title in 1984 and seventh major, he would never win another one?

“I didn’t think that would be my last one,’’ McEnroe told The Post. “It’s obviously disappointing and I had to, over time, accept that. It wasn’t easy. I still felt I could do it for a while. I was waiting for it to click in. It just didn’t.’’

In 1984, tennis analysts were in agreement: Despite being tennis’ tempest, McEnroe would wind up as the greatest ever with his brilliant serve-and-volley grace. How fleeting greatness became as the Pete Sampras-Andre Agassi era was beginning.

McEnroe took a six-month hiatus in 1986 to “regroup,” tried yoga and weight-lifting and played less doubles. But he never regained his massive superiority.

“People were saying that [in 1984] I was on the way to being the greatest,’’ McEnroe said. “It’s easy to be a backseat driver. Instead of trying to move forward and improve my game, I felt I waited to see what other people would do. That ended up costing me. I didn’t add to my game — change my forehand, hit it subtly different. You need to look to add something.’’

McEnroe is considered the greatest tennis broadcast analyst in history, but no longer a top-five all-time selection as a player.

The clear-cut top five is headed by Roger Federer, Rafael Nadal, Novak Djokovic, the so-called “Big 3’’ who are 1-2-3 in Grand Slam titles. Throw in Pete Sampras and Rod Laver, who won the last men’s Grand Slam 50 years ago.

McEnroe then is in a battle with Bjorn Borg, Jimmy Connors, Roy Emerson, Bill Tilden, Ivan Lendl and Agassi. What should count for something is McEnroe’s magnetism in drawing fans to the game and his bringing a pure beauty and artistry to the game that every bit rivals Federer.

Also, McEnroe often skipped the Australian Open.

“I keep dropping in the overall rankings,’’ McEnroe said. “I’m hoping I’m in the top 10. I’m hopefully somewhere between seven to 10.’’

McEnroe is grinding on the senior circuit, fitter than he could have imagined at 60.

“It’s still deteriorating rapidly,’’ McEnroe said. “People were telling me, ‘Wait till you get to 60’. I love to play. I wished l loved it then like I do now. But it’s the movement, recovery, everything.’’