Happy Valley couldn’t have been a happier place 15 days ago when Penn State came from 21 points back to beat Northwestern 35-21 for coach Joe Paterno’s record-setting 400th triumph as the Nittany Lions’ head football coach.

Paterno’s big triumph came on the 141st anniversary of the memorable Rutgers 6-4 victory over Princeton in New Brunswick, N.J., Nov. 6, 1869, the game that is generally acknowledged as the first American football contest.

Anyone who can coach football at one institution for 61 seasons, including 45 as the man in charge, and win 400 games as the head coach leads one to believe he may be blessed with the “Methuselah Gene.” And the way Paterno keeps rolling along like Old Man River, he may be around as long as Methuselah while winning a few hundred more football games.

Joe Paterno, who will turn 84 next month, was just a kid from the Flatbush section of Brooklyn who was a winning quarterback at Brooklyn Prep and then Brown University during the 1940s. Stanley Woodward, the renowned sports editor of the New York Herald-Tribune back then, wrote of Paterno, “He can’t run and he can’t pass. All he can do is think — and win.”

Paterno has been thinking and winning ever since to the point where he holds records that will last a long time.

The 400 triumphs are the most by any coach in what is considered the elite or major college football competition. Penn State has always been a major football power. It was in Division I when Paterno first went there in 1950 and when he became head coach in 1966. Major college football was called Division I-A in 1979 and is now listed as NCAA Division I Football Bowl Subdivision.

Joe Gagliardi, of St. John’s University in Minnesota, holds the collegiate record of 478 victories as a head coach. All of his triumphs were at two NCAA Division III institutions. The late Eddie Robinson won 408 games as the head coach at Grambling State in Louisiana, a historically black institution that is in the NCAA’s Division I Football Championship Subdiv-ision, formerly Division I-AA.

Long ago Paterno passed Paul (Bear) Bryant, who had 322 triumphs at four major institutions, and Bobby Bowden, who had 377 victories before stepping down as Florida State’s coach after the 2009 season. Ironically, Paterno was never able to beat Bear Bryant in their four meetings as head coaches even though Penn State was favored over Bryant’s Alabama in three of those games.

Paterno also holds the record for most bowl victories at 24 and bowl appearances at 36. He is the only head coach to win in each of the original big four bowls — Rose, Orange, Cotton and Sugar. He also has a perfect 6-0 record in the Tostitos Fiesta Bowl, now the fifth “big” bowl.

Paterno was taking his teams to bowl games regularly back when there were only 10 bowls for major teams in the late 1960s. The Fiesta Bowl did not exist until 1971. Now there are 35 bowls so the majority of major teams play in a bowl, whereas 40 to 50 years ago a bowl appearance was a considerable accomplishment.

Paterno has always been a strong advocate for a major college football playoff and has spoken out strongly about this issue year after year.

But that is Joe Paterno. You never have much doubt about where he stands on any issue.

Because of this tendency to be heard and be very outspoken, Paterno has made some enemies at other institutions and even on his own campus, where he argued strongly with more than one Penn State athletic director over the years.

Sometimes expressing himself with rather acerbic comments, Paterno probably cost Penn State a chance to join the Big East Conference years ago when that league was beginning to expand in the 1980s. Instead, Penn State landed in the Big Ten in 1993, where I feel Penn State does not fit.

But then, despite a lasting friendship with Paterno that goes back over half a century, I have disagreed with him on numerous matters while covering intercollegiate athletics and Penn State football games in particular.

I lived in and attended public high school in the Park Slope section of Brooklyn when Paterno was going to a parochial school in nearby Flatbush. But we never met until I first reported on Penn State football in the 1950s.

I enjoyed every minute of my association with this man, so much so that four decades ago I teamed up with the late Merv Hyman, a fine reporter and editor at Sports Illustrated, to write a book, “Joe Paterno: Football My Way.” Following is a paragraph from that book, published in 1971:

“Joe Paterno has taken on the President of the United States publicly; he has blasted the National Football Foundation and Hall of Fame for ignoring his two unbeaten teams (1968 and 1969) when that organization awarded its MacArthur Bowl for the national championship to other teams; he has often taken exception with his colleagues in the American Football Coaches Association; he has criticized Ivy League football (he played in the Ivy League at Brown); he has barred the press from some of his practice sessions but then, in an unusual display of open-mindedness, he has called in those press members who regularly cover Penn State, for a frank briefing on special offensive and defensive plans the night before important games.”

He was not cast from any coach’s mold seen before he came along.

Paterno emphasizes academics with ­football, and it shows as the Nittany Lions’ football player graduation rate always ranks among the top three or four in the NCAA. But this doesn’t mean Paterno and his players are perfect. Like any other coach, Paterno has had his serious problems with player misconduct. This ranges from simple drinking problems on campus to very serious charges of crimes by players.

But going back to when he was an assistant coach under Rip Engle, 1950-1965, Paterno was profoundly involved with and helped mold the lives of such outstanding players and graduates as Milt Plum, Lenny Moore, Rosey Grier, Dave Robinson and others before becoming head coach in 1966. Then he was the boss and chief mentor for the likes of Mike Reid, Steve Smear, Dennis Onkotz, Jack Ham, Charlie Pittman, Lydell Mitchell, Franco Harris, Ted Kwalick, John Hufnagel and John Cappelletti, the 1973 Heisman Trophy winner. And these were just an example of Paterno’s best players in his first eight years as head coach.

After that, along came the likes of Todd Blackledge, Chuck Fusina, Kenny Jackson, Matt Millen, Mickey Shuler, Curt Warner and many, many more outstanding players.

Just as he helped these players progress to success, they worked hard and played hard to pile up all these victories for Paterno even though not every one of them loved him or enjoyed his sometimes harsh attitude and strict rules. Paterno’s approach is that practice is hard work so that Saturday’s game can be fun.

Throughout this long journey of success, Paterno has been aided by his favorite person in this world — his wife, Sue. Despite making a fortune worth millions of dollars, they still live in the house, just a couple of blocks off the Penn State campus, where they raised their five children who, in turn, have given Joe and Sue 17 grandchildren.

Joe and Sue have donated millions of ­dollars to Penn State libraries, athletic facilities and other Nittany Lion needs.

Joe Paterno is a very unique personality in this world of college athletics where we see so much hypocrisy and corruption. He has always cried out against such things in his very strong Brooklynese.

When I first began writing extensively about Paterno even before he replaced Rip Engle, my sports editor at The New York Times, Jim Roach, asked me one day, “Why is this guy so different and so special?”

My answer: “I guess it’s because he comes from Brooklyn.”

Gordon White served 43 years as a sports reporter for The New York Times. His e-mail is sports@thepilot.com.