But unlike most of those years, the once spry Duncan is now - at least in the eyes of some - old. The white hairs that now sprout from his black beard make that apparent. But instead of going into denial about his age and shaving the beard, Duncan accepts it. After all, the soon-to-be 36-year-old and future Hall of Famer has never been one to go against the grain.
And that certainly holds true with his role on the Spurs. No longer the centerpiece of the Spurs success, Duncan has embraced his role on the team as his game has changed, and the Spurs are seeing positive results.
But while Duncan may make this change seem easy, he's quick to say that's not the case.
"I'm a competitor just like everybody else and you don't like to see your role change," Duncan told CelticsBlog. "But honestly, if things are affected and things are working, I'm happy to be a part of whatever we come up with."
Duncan, who realized he was no longer Option No. 1 "years ago", was unsure what type of player it takes to put the ego behind and let others step in, but his message rings true in all facets of life - "At some point you have to be realistic and accept it."
That doesn't mean rolling over and dying. It just means accepting change for what it is and making the best of it. New role, same give-it-your-all attitude.
Sound familiar? The Celtics' Kevin Garnett, now in his 17th season, made that we-before-me transformation when he joined the Celtics. The result? A championship in his first season with the team. Garnett, who peaked at just under 20 shots per game with the Timberwolves during the 2003-04 season, is now averaging under 13 shots per game this season with the Celtics (although he took 19 Wednesday night).
Compared to the rest of the NBA, his numbers won't wow you. But Garnett has transcended his game this season, proving to everybody - everybody - that he's still got "it", whatever that "it" is for him now.
It's easy for Spurs coach Greg Popovich to see.
"He's like Timmy [Duncan], you know? Fine wine," Popovich said of Garnett. "They figure out what they need to do, they know what they do well, they know what they possibly don't do as well as they used to. So they figure out new ways to do things. They both have high basketball IQ's, and you see them both having very good seasons."
Better with age is a bit of a stretch, but the appreciation of each player grows with each game. Garnett currently ranks 18th all-time in scoring, Duncan 25th. In terms of total rebounds, Garnett 12th, Duncan 18th. There are no active players ahead of them, and there are no active players even close to behind them.
That's due to their attitudes and work not only on the court, but off.
"They're so different in the way they play, but they're very similar in the way they approach the game," Celtics coach Doc Rivers said. "I think they're as professional as we've seen for stars maybe ever at the same time. You rarely get two superstars at their level that are as coachable, and are as team-oriented as those two guys. Again, they do it completely different ways. Tim never talks - he talks more than you think, but you don't see it. Kevin on the floor, you see all his stuff, yet they still do it for the same reason."
Could last night's game have been the very last matchup between the two players? Garnett and Duncan are both unrestricted free agents after this season, and their futures in the NBA are uncertain. Retirement is an option, although both have shown they still have plenty of basketball left in them.
Garnett went for 16 points, seven rebounds, and five assists Wednesday night, and Duncan scored 10 points, ripped down 16 boards, and blocked three shots. The two went at it much like they have since Duncan joined the league a couple years after Garnett.
"It's been difficult," says Duncan of matching up with Garnett over the years. "We've always had some great battles. It always seems to turn into a war at some point in the game. But it's a lot of fun. I think we bring a lot out of each other."
Garnett's words were more to the point - as usual.
"It's been tough but fun at the same time," he said. "Competitive. There's never a dull moment."
Primarily power forwards throughout their respective careers, both players have made the transition to center as of late.
"I mean we are both older," Duncan admitted, "we're not the go-to guys so we are kind of matched up more and we're both kind of playing more center, so it just happened that way and as usual it's tough playing against him."
Mid-thirties or not, both Garnett and Duncan still have championships on the brain. The Spurs (38-14) are the hottest team in the NBA right now, and the Celtics (30-23) have started to click in the second half. For both guys, another ring is the only thing - and adapting to their roles for the betterment of the team is an integral part of achieving that goal.
"It's important for me to get another four championships," said Duncan when asked of the importance of winning another championship. "But is it going to happen? I don't know. Probably not. I'm going to play it out and play as well as I can, and luckily I'm on teams that have the ability to push for championships. And that's what you want year-in and year-out. Nothing's guaranteed and nothing's promised. I'm just here to play as much as I can."
There is one guarantee though. Whenever Garnett and Duncan do decide to hang ‘em up, the mark they've made on the game will remain forever.
But as for now, enjoy it. They seem to be.