WALTHAM, Mass. — Boston’s Isaiah Thomas is feeling like a new man. A taller man.

“I’m now listed at 6-1,” the 5-foot-9 point guard joked when he sat down at Celtics media day on Monday. “I grew a couple of inches this summer.”

While Thomas was speaking in jest, there’s nothing at all fake about his excitement entering this season.

The Celtics went into this past offseason focused on attracting the kind of star power to their roster that would help them move into the contender ranks of the Eastern Conference.

They missed on Kevin Durant, but added veteran All-Star forward Al Horford to a young core that already includes Thomas — a first time All-Star himself last season — Avery Bradley, Jae Crowder and Marcus Smart.

It’s given coach Brad Stevens a lot to work with entering training camp as he tries to help Boston advance past the first round of the playoffs for first time since 2012.

“We’re not asking Al to be any more than him,” Stevens said. “He’s a good fit for how we play on offense, he’s good fit for how we play on defense…he’s a guy that guys can follow by example. It’s unfair to ask Al to be anything more than who he is.”

Who the Celtics have been the past two seasons is one of the surprise teams in the East. They improved from 25 wins in Stevens’ first season in 2013-14 to 40 and 48 wins the past two seasons, which both ended in playoff berths.

Boston pushed the Atlanta Hawks to six games last season despite losing Bradley to a hamstring injury in Game 1 against the Hawks, seeing big man Kelly Olynyk aggravate a shoulder injury in the same game, and watching Crowder struggle throughout the series because of an ankle issue.

Having a promising year derailed by that kind of bad luck has stuck with Thomas.

“All season that’s all I thought about,” Thomas said. “Losing that series left a bad taste in all of our mouths. We want to get past that first round. I do, I know that. I want to win a playoff series. I want to go farther; we have a good enough team to make that happen.”

Gone are sixth man Evan Turner and Jared Sullinger, who both left in free agency. But the optimism and excitement surrounding Horford was palpable Tuesday. Not only for his ability to defend and be a big man who can stretch the floor, but for his anxiousness to see the Celtics return to a championship contender.

His four-year, $113 million deal certainly carries with it some weighty burdens, but he said he isn’t feeling any pressure because of it.

In his very first trip to the Garden as a rookie in 2007, Horford recalled being mystified by Celtics’ championship banners hanging from the rafters.

“You’re very aware,” Horford said. “I couldn’t stop looking at the banners up top. Maybe some guys feel differently, but I couldn’t stop looking at them. It’s something that’s powerful. It leaves an impression on you.”

Team president Danny Ainge said he thinks Horford is joining a team that already has garnered the attention of other teams around the NBA.

“We’re not going to be able to sneak up on anybody,” Ainge said. “I think that the team has earned a great deal of respect around the league the way they played last year, and the last couple of years. That’s a good thing. That’s progress. That’s where we want to be. We want our expectations to be higher. And learning to live up to those expectations is part of the grind.”

This month will be about integrating Horford into that foundation.

It’s a challenge Horford says he’s eager to embrace.

“I have a good idea of the history of the Celtics, and of the passion of the people here. I know that it’s special, and that’s part of the reason that I’m here,” he said. “I want to be a part of that.”

Notes: Olynyk, who had arthroscopic surgery on his shoulder in May, is due to have his five-month evaluation on Oct. 15. But he has been cleared to do noncontact drills in the interim. “Hopefully in the next three or four weeks, I can get out there and make something happen,” Olynyk said. “I just gotta make sure it’s strong enough to take the hit.” …Stevens said that he has had discussions with players and other team officials regarding the protest and demonstrations that have taken place during the national anthem in the NFL and other sports. “It’s been great to engage in those discussions. It’s been really fun for me to hear about how excited our guys are about using their platforms to promote good things,” Stevens said.

Follow Kyle Hightower on Twitter at http://www.twitter.com/khightower