Leonard Williams turns 23 next Tuesday, but he is already a veteran leader in the Jets’ young locker room.

In an offseason that has seen years of experience and leadership walk out of the door as they tear down their roster, Williams’ development as a team leader has taken on more importance.

The good news is Williams knows it.

The third-year defensive lineman spent this offseason taking a course at the Ascension Leadership Academy in San Diego. Williams and his girlfriend, Hailey Lott, took the course at the urging of Hailey’s father — Ronnie Lott. Yes, that Ronnie Lott, the Hall of Fame defensive back who led the 49ers defense to four Super Bowl titles.

In his first two seasons with the Jets, Williams has shown he can play. He made the Pro Bowl last season and was the team’s best player. Now, he is trying to fill the leadership void left by the departures of Darrelle Revis, Brandon Marshall, Nick Mangold and, in the last week, David Harris and Eric Decker.

“I think it’s just great to have as many leaders as possible,” Williams said. “That’s something we’ve tried to harp on. After your first day, you’re not a rookie anymore. Even to the younger guys, we’re telling them it’s never too early or too late to be a leader.”

With that in mind and at Lott’s urging, Williams and Hailey, a meditation and yoga instructor, signed up for the ALA course in San Diego. The course is taught over five weekends. Williams will return for his final sessions later this month.

“It’s an environment that provides an opportunity for you to create a new perspective about who you are and what you’re truly capable of,” the ALA website says.

Williams said the classes are filled with people from all types of professions, not just pro athletes. He said the people learn from each other and discover things that hold them back from fulfilling their potential.

“I just learned it’s all a mindset,” Williams said. “I’ve kind of already known that, but they just harped on that a lot. Everything that you think is possible you can make possible, things like that. … It helped me go to work every day with a purpose.”

Williams’ leadership skills were on display in a way he probably wished was kept private recently. When Darron Lee had a heated argument with his girlfriend at a concert on Randall’s Island two weekends ago, Williams got between them and then picked Lee up and literally removed him from the situation. He showed the power his 6-foot-5, 302-pound body holds.

Williams declined to comment on the incident, but he did not need to. The video posted on social media told the story. He was looking out for a teammate, like any good leader would.

The release of Harris last week hit everyone in the Jets locker room hard, but particularly the defense. Harris has been the leader of the Jets defense for as long as anyone in the locker room can remember. He set the tone on the field as the quarterback of the defense and off the field with the way he worked and carried himself.

Williams, the Jets’ first-round pick in 2015, was always watching and learning from Harris.

“He just taught me how to show up ready to work every day,” Williams said. “He was the first one in, the last one out always. He played every day as hard as possible. I loved seeing that from him. He was an older guy, already established. He still showed up to work every day as if he was a rookie. I loved that.”

Now, the young players will be looking to Williams to show the way.

The Jets are a team in flux, but Williams feels like a sure thing — maybe the only sure thing on the roster. The “Big Cat” is now at the core of this rebuilding team. Maybe Jamal Adams and Lee will be with him. Maybe another player from USC will join him next year in Sam Darnold.

For now, though, this is Williams’ team, and he looks ready to lead the way.