ENGLEWOOD, Colorado — Ahmad Brooks is the grey beard of the 49ers defense, a 32-year-old outside linebacker who is one of the last survivors of their 2012 season’s Super Bowl run.

What is he still doing there, amid the franchise’s obvious rebuild?

Brooks represents the 49ers’ best chance of sacking quarterbacks, at least through the season’s first four games while Aaron Lynch serves a suspension for substance-abuse.

Brooks won’t disagree with that assessment.

“I believe in my heart that I’m one of the best football players in the NFL today, regardless what position I play,” Brooks said this week. “That’s how I’ve been my whole life: I’ve just been one of the best guys on the team.”

He looked like one of the best Thursday in a joint practice with the host Denver Broncos. He produced a would-be sack of Mark Sanchez and nearly intercepted rookie Trevor Siemian, who will start Saturday night’s exhibition.

It’s the second straight year the 49ers worked out at the Broncos’ facility on back-to-back days prior to an exhibition. But Brooks didn’t stick around for last year’s follow-up practice.

A year ago, Brooks had to fly home before that Thursday’s practice, having been charged by Santa Clara County prosecutors with sexual battery in a December 2014 incident with a woman at former 49ers Ray McDonald’s house.

His tenure with the 49ers was in jeopardy, as was his legal freedom, of course. Brooks has not discussed the case as it weaves through the judicial system. A July 18 pretrial conference was continued to Nov. 21, according to prosecutors.

Trent Baalke, the 49ers general manager, wasn’t aware of Brooks’ legal standing when the topic came up Wednesday during an interview. Nothing new has happened regarding the case since Baalke and the 49ers aligned themselves with Brooks amid his troubles.

“Ahmad and I, along with ownership, we sat down and had a great visit when Ahmad was going through a lot of this,” Baalke said. “We listened to him. We dug into the situation. We decided it was in the best interest in all of us to stand behind the player.

“He’s made some mistakes; he’s well aware he’s made some mistakes,” Baalke added. —… I couldn’t be happier with the progress he’s made off the field. He’s done everything asked of him.”

On the field, Brooks had a sack, three tackles and chased down a running back in Sunday’s opener.

Brooks’ 45½ sacks since 2009 rank him fourth on the 49ers’ all-time list of sack leaders. His next regular-season sack will tie him with Dana Stubblefield for third place behind Bryant Young (89.5) and Charles Haley (66.5).

“What Ahmad does really well is his feel for football,” outside linebackers coach Jason Tarver said. “When he starts with speed and feels blockers, he’s really good at seeing and bursting from that blocker to get to the quarterback.”

Such moves come with experience. As Brooks enters his 11th season, he’s already passed his rookie goal of lasting 10 seasons, and he now watches film to confirm he’s still a high-caliber player. Keeping his body fresh isn’t as easy, however.

“Man, I know I’m 32 years old, and this is my 11th year, so the things I was able to get away with before, I can’t now,” Brooks said. “So I have to keep that in the back of my mind as far as maintenance, rehab, hot tub, and cold tub — my best friend right now.”

Brooks isn’t exactly surrounded by long-time friends on the defense. Since 2014, there’s been a wave of departures, replaced by a surge of first- and second-year players.

“They keep me young,” Brooks said. “A lot guys on the team don’t think I’m 32 years old. They think I’m 27 or 28. I’m like, ‘What?’

“I guess it’s the way I act because I don’t seem like I’m old. That’s how I approach this game — I try to stay kid-like as much as possible.”

Now it’s up to Tarver, new coach Chip Kelly and new defensive coordinator Jim O’Neil to tap into whatever Brooks has left in his career. Baalke said the coaches are “very pleased” with Brooks’ transition to the new defensive system.

“He looks to have a lot of gas left in the tank,” Baalke added.

Added Tarver: “He likes where we’re headed with the scheme overall, and also with the youth and the competition around him.”

Brooks and Lynch shared the team lead in sacks each of the past two seasons. But they only totaled six sacks in 2014 and 6½ last season, numbers that pale in comparison to Aldon Smith’s totals in 2011 (14 sacks) and 2012 (19½) .

Brooks believes 6-8 defensive tackles Arik Armstead and DeForest Buckner will bolster the entire defense’s pass rush.

“Pass rush isn’t just about one man,” Brooks said. “You’ve got to look at the time Aldon was getting all those sacks. It wasn’t just Aldon Smith beating the guy one on one. It was Justin Smith on the same side as him.

“I’m excited for this year, not just for me but everybody else.”

For more on the 49ers, see Cam Inman’s Hot Read blog at blogs.mercurynews.com/49ers. Follow him on Twitter at twitter.com/CamInman.