Their faces are pockmarked with ever-expanding wrinkles, their bodies seem to ache all the time - the telltale signs of an athletic career marching glumly toward its final chapter.
Yet there's a bounce the steps of Boston's Big Three, a determination in their eyes, an overwhelming sense that they aren't going to let this partnership go down without one helluva fight.
They are still underdogs to LeBron & Co, but Team Geezer may have one last hurrah, after all.
"Early on in the season, when we were losing, people were getting conditioning mixed up with age," coach Doc Rivers said Monday, an off day in the Eastern Conference final. "They kept saying we were too old and I'd say, 'No, we're out of shape. We'll find out how good we are later.' I didn't really know, either, but sometimes, as a coach, you have a feel about a team. I know we're a good team and we can play with anybody."
Four games into a series the Miami Heat surely thought would be firmly under control by now, and it's all tied up. While LeBron James desperately wants to win his first NBA title - and his team still has home-court advantage, it must be noted - the guys in green are playing with an even greater purpose.
There may be no country for old men, but there may be room for another championship in Beantown.
"We have a chance of winning this series," said 34-year-old Paul Pierce, who's nicknamed "The Truth" and knows how to speak it. "It's not going to be easy. You know, a good ol' classic bar fight. Going into it, you've got to expect every game to be like this. Coming down to the wire, both teams trying to find an edge."
Around the nation, they're jumping on the bandwagon.
ESPN recorded its highest cable rating ever for an NBA playoff game Sunday night, as millions tuned in to watch the Celtics hold off the Heat 93-91 in overtime, an especially gutsy performance by a team that absolutely oozes with that particular trait.
Sure, there's plenty of people who just want to see James and Miami's own version of the Big Three go down in flames again, and there was plenty of chatter about the King passing up another potential game-winning shot.
But there's more to it than just the anti-LeBron factor. Admit it, anyone who lives outside of South Beach, San Antonio or Oklahoma City:
The Celtics have become America's Team.
At the very least, they're the team representin' a very hefty portion of America that's been told, "Hey, ol' dude, call it a day. It's time to let someone younger take your place."
There's Pierce, still sporting that old-school headband and perpetual grimace. There's 36-year-old Kevin Garnett, still banging and trash-talking after all these seasons. There's Ray Allen, also 36 and still launching those smooth jumpers, even with an ailing right ankle that was headed for a date with a scalpel just a few weeks ago.
"It starts with our leadership," backup Keyon Dooling said. "We have a bunch of gritty guys. Our superstars are gritty. They wear their hard hat everyday and come to work. They set a tone and set a tempo for our whole team."
Well, actually, the tone is set by Rajon Rondo, the otherworldly point guard who is performing like someone who got a huge mulligan in these playoffs. He was kicked out of the very first postseason game against Atlanta for bumping an official, and had to serve a suspension in Game 2. But the short-handed Celtics managed to win that contest, which was essentially the margin of their six-game triumph over the Hawks.
Since then, Rondo has played like he's still trying to make up for losing his temper. He's averaging 17.4 points, 11.9 rebounds and 6.8 rebounds in the playoffs, carrying the Celtics on his younger, stronger back much of the time.
But ceding the spotlight to Rondo is perhaps the greatest measure of the Big Three's greatness.
Sure, they're all still key performers, just not as much as they were during Boston's last championship run in 2008. When it's time to get out of the way and let Rondo work his magic, that's what they do. Which explains why they're six wins shy of a championship, even with Pierce fouling out in three of the last five games.
"Last year, we would've been out of the playoffs already," Rivers said. "It just wasn't the same. We weren't a team. This is a team. We're very close, very competitive. I think they kind of understand now that Rondo is the leader of the team. Everyone else plays off Rondo."
Boston has to like its position. This is the ninth time the Big Three has gone to a Game 5 tied at two games apiece. Their record up to now: 8-0.
Of course, only one of those wins was on the road, which is where they'll be playing Tuesday night. And winning Game 5 is not even a guarantee of ultimate success, since the Celtics went on to lose twice after going up 3-2. But that one road win, interestingly enough, came against James and the Cleveland Cavaliers in 2010.
If the Celtics knock off James' new team in another Game 5, we have no doubt they'll wrap up the series, and a trip to the NBA Finals, two nights later.
Rivers keeps insisting that he never tries to spur on his trio of aging stars by reminding them what awaits. He doesn't have to. They're wise enough to realize that time marches on and it's running out on them, as it will for all of us.
But this could be one of those rare times - like George Foreman winning a heavyweight title in his 40s, or Jack Nicklaus willing himself to one last Masters title - when resolve wins out over reason. There's nothing logical about the Heats losing this series to the Celtics. But, with each passing day, we can envision it happening.
What is more important, the Celtics can envision it, too.
Time is standing still, if only for a moment.
"I just think they're playing hard and great because they believe they can win," Rivers said. "I figure guys like that have a pride in themselves anyway and don't really need me to say anything."
Paul Newberry is a national writer for The Associated Press. Write to him at pnewberry(at)ap.org or www.twitter.com/pnewberry1963