For the first time since his rookie season, Kevin Garnett spent the All-Star break away from the game and alone with his thoughts. He thought about the first half of the season and what went wrong. He thought about what he could do better. Garnett decided that he had to make changes.

“The first half of the season wasn’t the most pleasurable for us,” Garnett said. “I thought I could be better and I’ve been working toward that. I’ve been giving myself a true analysis in the mirror. Looking at myself, telling myself what can I do better and I’ve been going toward that. It doesn’t take much to motivate me.”

One of the things that did motivate Garnett was the notion that his best days are behind him.

“I hear you all calling me old,” he said. “I hear you calling me, um, older. Weathered. I’m motivated. It don’t really take much to motivate me, man. I’m older in basketball years, but in life I’m 30-something.”

Garnett may not relish knocking heads with the likes of Andrew Bynum or Dwight Howard, but those two are few and far between. The league is filled with quasi-centers like Al Jefferson, whom Garnett tangled with in the Celtics’ 94-82 win over the Jazz on Wednesday.

Jefferson shot 1-for-8 in the first half against Garnett, but battled him throughout the second. Garnett got the better of the matchup, scoring 23 points to go with 10 rebounds – his 16th double-double of the season.

At one point they each received technicals after a post-whistle dustup. Asked about it later, Garnett feigned disinterest, but didn’t make an effort to hide his grin. He loves going up against the young guys and proving that he still has it.

“They clearly have something,” Doc Rivers said. “That’s how it always is. Al was traded from here and Kevin is here so that will always last. I thought it brought out the best in KG, no doubt about that. That was good.”

Along with the self-analysis, the other big change for Garnett has been a move to center. This has been an evolution long in the making, although Garnett has stubbornly resisted the moniker. He’ll tell anyone who asks that he’s a four, and always will be a four, but of course that’s not what he is anymore and it’s been a boon to both him and the Celtics.

“Kevin’s been amazing,” Rivers said. “If you had an All-Star vote at the center spot in the league right now he’d be right up there. That’s what he’s been since the break. He’s a five and he’s been terrific. Don’t tell him that.”

All of this leads to an interesting conversation for the Celtics to have after the season. With Dwight Howard off the market, Garnett is suddenly the best unrestricted free agent big man available. (You can throw Tim Duncan into the conversation as well, but it would be a shock if he ever seriously contemplated leaving San Antonio.)

Considering how durable Garnett has been this season, and really how durable he’s been since his offseason knee surgery in 2009, wouldn’t it make sense for the Celtics to try and bring Garnett back for say, two more years while Danny Ainge retools the rest of the roster?

With two picks in the first round of this year’s draft along with developing players like Avery Bradley and Greg Stiemsma, Ainge can still build a competitive team around Paul Pierce, Rajon Rondo and Garnett for the present while also allowing the unproven talent to work its way into the league on a team that epitomizes professionalism.

There are few better mentors for young players who want to work than Garnett, who has praised the young players on this year’s team and they have been eager to soak up the knowledge. “Kevin is constantly trying to help everybody get better,” Bradley said. 

Rivers nodded indirectly in that direction when asked about the Jazz, who have a combination of young talent and veterans. “It’s the way to have a team,” Rivers said. “I’ve always thought if you want to restart a team, you don’t do it all young. That just doesn’t work. I think the only place it’s working is Oklahoma City and they have a guy named [Kevin] Durant that probably helps in that and everybody else follows – [Russ] Westbrook, as well.”

No, the Celtics don’t have Durant and they’re not likely to get anybody close to his ability this summer. But they do have Garnett and they have been built around him in small, subtle ways.

The switch to center was part desperation and part inspiration. With no other healthy bigs on the roster, he was the logical choice, but it also made basketball sense. He and Brandon Bass are two of the best outside shooting big men in the league. That stretches the defense and lacking one-on-one creators, the Celtics are reliant on space to make their halfcourt offense work.

In the past, Ray Allen was responsible for creating much of the space with his constant movement, but times are changing and now it’s Garnett’s ability to step out against larger, and usually slower, defenders that opens things up for the rest of them.

Garnett is shooting more, but it’s where he’s shooting from that’s so important. Per HoopData, Garnett is taking seven shots per game from 16-23 feet, up from about five attempts earlier in the year, and that number has been steadily increasing.

“Well, I think he’s taken it upon himself to be more aggressive,” Pierce said. “He’s not hesitating, he’s taking a lot of shots. He’s getting 18-20 shots on a consistent basis. We want him to be aggressive and he understands that’s what we need from him if we are going to be successful.”

Stubborn as he is, Garnett wouldn’t acknowledge that he’s been looking for his offense more. He noted Allen’s absence as a reason for his increased attempts and suggested that when Allen returns from an ankle injury he’ll go back to being a defensive-minded player. Maybe, but the Celtics have become reliant on Garnett’s high-post game.

Here’s another way the shift to a Garnett-focused offense has helped. The Celtics have gone 13-5 since the All-Star break, and one of the reasons has been a decrease in turnovers. You can credit Garnett for part of that.

“The only big we throw it to is Kevin, above the elbow,” Rivers said. “Basically it’s that simple. Before we were running all this elbow offense, but it was any big and we realized that maybe Kevin should be the only ball handler above the circle.”

Garnett will have more soul-searching to do this summer. In the past, he’s hinted at retirement when his contract expires, but now that it’s coming closer those hints are growing fainter. He’s already adapted and evolved to the point where he cannot only continue to play, but continue to play at a high level.

Will it be here in Boston? That’s a question he’ll have to answer, but the door seems to be open and it’s hard to make a case that the Celtics would be better off without him.