The Celtics have been "getting old" for so long that it has become cliche. On the whole it isn't even an accurate description anymore because the team has brought in so many younger players to support the core that the average age is probably in the middle of the NBA pack anyway.
However, in case you missed it, Paul Pierce, Kevin Garnett, and Jason Terry are 3 of the biggest pieces of our core squad and they are all over 35 years old. I happen to be 37 myself and while I'm not a professional athlete, I can attest to not being able to do the things on the court I could do when I was a strapping twenty-something... at least not more than once in a blue moon. So it begs the question. Can this team still be consistently good?
What defines a "good" player if not consistency? Anyone in the NBA can have a good game (however you measure what good is for that particular player). What sets the very good and great players apart is being able to do it night in and night out? Rookies seldom come into the league being able to dominate every night. They have their ups and downs as they learn the NBA game. Bench players and role players typically are what they are by the time they hit their primes, but even they can have a very good or great game from time to time. Then there are the older players.
When stars get old, they often still bring that same drive, intelligence, and skill that made them great, but they can't physically do all the things they once could. That reservoir of energy and burst isn't as deep as it once was and the lift and quickness are just not quite there anymore. This is what people mean when they say a player is "a step short." They can't explode past their man anymore.
Paul Pierce was never an athletic marvel, but he was sneaky quick and had some hops when he really needed to use them. Now he looks particularly Earthbound and relies heavily on picks and screens to get open looks. Kevin Garnett was once an athletic freak, but has modified his game to the point where he can still dominate without jumping over people. In particular his greatest skill is to know just where to be on defense and get their faster than the opponent can. Still, Doc wouldn't have him on a strict minutes limit if it wasn't for his own good. When he's left out there too long, he simply can't get to where he wants to be and everything breaks down.
I'm not as familiar with Jason Terry's game, but I'm sure you could find examples of why he's great on some nights and not so wonderful on other nights - and more often than he used to be.
So we've got a team where 3 of the best 4 or 5 players are over 35 and thus prone to having off nights or at least quiet quarters or halves. Then you've got the rookies and bench players who are inconsistent by definition. So the only consistent player is our new leader and best player Rajon Rondo (warning, flammable). When he has help the team looks like world beaters, like they did against the Thunder. On nights when the rest of the team is up and down, he can only do so much to will the team to victory. Especially when he's a facilitator by nature.
Back in 2008 it was Rondo that was the inconsistent one. He was capable of triple doubles on some nights but also very capable of games where he scored 2 points and managed just 4 assists. Coupled with the offensively challenged Perkins there was a lot of heavy lifting left to the Big 3. They were on the back 9 on their primes but they could still do it most nights. That was 5 years ago and they can't carry dead weight anymore.
The older players need more help and that help has to come from players that are going to be inconsistent. Jeff Green isn't going to score 19 points a night. Brandon Bass isn't going to get a double double on most nights. Courtney Lee can't be counted on every game - at least not on offense. What we can hope, however, is that these guys can step it up on defense.
Garnett can't cover up for everyone's mistakes and Pierce can't guard quick 2's and 3's as consistently as he could back in the day. But if this team can hit their spots more often from top to bottom, then they can get back to playing the best defense in the league again - no matter the age of anyone on the floor.
The points will come on offense as long as Rondo is conducting the orchestra. But they have to get stops more consistently and in particular when Garnett is off the floor. We don't need Green, Bass, and Lee to be a mini-Big-3 offensively if they can step up defensively. Same goes for anyone else on the roster that sees floor time.
So the trio of Pierce, Garnett, and Terry is undoubtedly getting old. But they can still bring it enough that if you give them a chance, they'll win the games more often than not. They just need their teammates to help them carry that burden and get them within striking distance at the end and it has to start with defense.