PITTSBURGH — At 35 to begin the season, Casey Hampton, by NFL standards, is old.

Generously listed at 325 pounds, coming off knee surgery and on the physically-unable-to-perform list, Hampton is, at the moment, slow.

But the nose tackle says it’s far from over — for him or for the Steelers defense.

More than 10 months ago, Warren Sapp went on Showtime and labeled the Steelers defense “old, slow and it’s over.” Pittsburgh since has released the unit’s three oldest players, leaving Hampton the eldest statesman on a defense that ranked No. 1 in the NFL last season.

Recovering from a torn ACL sustained during the Steelers’ January playoff loss in Denver, Hampton said a Pittsburgh defense that remains among the oldest in the league is far from over the hill.

“They’ve been saying that for how long?” Hampton said. “They’ve been saying, ‘You’re getting old,’ and all that for years, and year in and year out we do our thing. So I don’t see it being any different this year.”

Hampton was referring to the Pittsburgh defense in general. But he could have also been referring to himself.

Entering his 12th season, Hampton turns 35 on Labor Day. Only backup quarterback Charlie Batch is older among Steelers players. But Batch spent the first four seasons of his career with the Detroit Lions, leaving Hampton the only Pittsburgh player who was around for the opening of Heinz Field in 2001.

Linebacker James Farrior and defensive linemen Aaron Smith and Chris Hoke retired during the offseason — as did receiver Hines Ward — leaving the stout Hampton no one left to figuratively look up to.

“No question about it, when you’ve been around those guys 10-plus years, it’s definitely different,” Hampton said. “But that’s part of it. You see guys come and go all the time. Those are definitely special guys, but I think those guys will fill in and do their best to make up for it.”

Steve McLendon is filling in for Hampton throughout these early camp practices, and Pittsburgh drafted Hampton’s eventual long-term replacement in April, University of Washington defensive lineman Alameda Ta’amu.

Hampton insisted his rehab is going well, saying “I’ll be ready to go” in time for the season opener Sept. 9 in a Sunday night game against Peyton Manning and the Denver Broncos.

Hampton was hesitant to estimate when he’d be able to come off the PUP list. Notorious over the years for his tongue-in-cheek anti-training camp stance, Hampton failed the Steelers camp-opening conditioning test in 2008. Coach Mike Tomlin put him on the PUP list as a result — a daring move for a coach who was in his second season against a veteran.

That season, Hampton often joked that he relished the time away from the two-a-days on the practice field. He’s not embracing it as much now.

“It’s different when you’re forced to miss it because of injury,” Hampton said. “You never want to be hurt and that to be the reason you’re on PUP.”

That said, Hampton doesn’t want to rush back.

“I don’t have no problem with being on it as long as I need to be. I just want to get it right and be right when I’m out there. I don’t want to be out there hobbling messing around; I wanna be out there ready to go.”

A first-round pick of the Steelers in 2001, Hampton became a starter almost immediately. Back then, Pittsburgh was one of only a handful of teams running a 3-4 defense — a system Hampton is perfect for at nose tackle.

His career statistics aren’t gaudy — nine sacks, 197 tackles (an average of less than 20 per season). But Dick LeBeau’s defense isn’t designed for the nose tackle to be making tackles or pressuring the quarterback. In layman’s terms, Hampton’s job is to take up space so that others get the glory.

“You’re kind of freeing (linebackers) up, making them make all the plays,” Hampton said. “Get your head up on the guy, try to draw the double-team, be as disruptive as possible ... And let the linebackers eat.”

Eating has gotten Hampton into trouble at times with Tomlin, most notably after the conditioning test in 2008.

In street clothes, Hampton looks slimmer than he has at many points over the past decade. He’s been working out on his own at St. Vincent College, rarely seen on the practice field even as most of the other Steelers PUP players are regularly on the sidelines during workouts.

“Every man out there, in their uniform or not, has a plan,” Tomlin said, “not only in the big scheme of things but daily and by a.m. and by p.m., and he’s no different than the others.”