Certain things are off limits no matter how physical it gets in the trenches of an NFL game.

But there were no penalty flags — just a scolding from Mom — whenever Nick Gates, his older brother by six years and two older cousins started roughhousing at their Las Vegas home.

Those childhood scuffles growing up in a “blue-collar family” where construction is the family business were the training ground for the undrafted third-year pro who Giants general manager Dave Gettleman keeps teasing as a potential answer to the uncertainty at center.

“My toughness comes from that,” Gates, 24, told The Post. “We used to go at it and I had to hold my own. I was the youngest [for a long time], so everybody kind of picked on me. You have to be tough when you are the youngest. Playing football or wrestling, one of us gets mad and it starts off from there.”

Gettleman mentioned Gates’ “bright future” without prompt in all three interviews he conducted from April 13-25.

“The thing you love about Nick is just how tough he is, because it’s a fist fight in there,” Gettleman said. “History tells you that the toughness of your team is really, really indicated by the toughness of your offensive line.”

About 2,500 miles away, Gates — such an infrequent social-media user that his Twitter bio still identifies him as playing for the University of Nebraska — heard the praise. He quickly tuned it out to focus on improving under new Giants offensive line coach Marc Colombo, who followed offensive coordinator Jason Garrett from the Cowboys.

“Colombo is a really good coach,” Gates said. “I like that he played [in the NFL] for 10 years. He understands that sometimes, when it gets tough, you just have to get the block — and that’s kind of how it happens. He loves teaching technique.”

A typical day for Gates right now includes two hours of virtual instruction, followed by three hours training at Phase 1 Sports facility in Las Vegas, which remains open only to professional athletes during the coronavirus pandemic.

The 6-foot-5, 307-pound Gates is in a group with Giants teammate Will Hernandez and a couple Raiders offensive linemen, taking his turn snapping to quarterback Derek Carr between lifting and running.

“It makes it a lot easier going to work out every day when you have those guys there to push you,” Gates said. “There’s a back-and-forth — I feed off their brain, then they ask me questions — that helps.”

Gates started 35 games at tackle at Nebraska but became a do-it-all backup for the Giants last season. After spending his rookie season on injured reserve (foot), Gates played in 16 games with two starts at tackle and one at guard, and practiced as a third-string center for the first time in his career at any level.

Now the Giants have a vacancy because center Jon Halapio is a free agent recovering from Achilles tendon surgery. Gates will compete against fellow returning backup Spencer Pulley, rookie Shane Lemieux and possibly a re-signed Halapio.

“I don’t mind it at all,” Gates said of changing positions. “If that’s where the team needs help, I’m ready to step up. The mental aspect is really the main load of center. It’s mostly a help position, but you have to point out where everybody goes and make sure everybody is on the same page. We’ll see when I get live reps with guys lined up three inches from me.”

Gates finally outgrew his older brother — a football player at Dickinson State — around his 18th birthday. When his younger brother by seven years finally was old enough to mix it up, Gates showed him no mercy.

“Everything runs downhill, right?” he cracked.

Sounds like a center’s mentality.

“It’s like a light switch. Once you are on the field, you have to turn it on,” Gates said. “Fletcher Cox, Aaron Donald, don’t care who you are. They are not going to take it easy. You have to bear down.”