While in New England among old friends last weekend, everybody kept talking about the Finals. This wouldn’t be news — except that they were talking about the 2009 Finals.

My pals figured that the 2008 Finals were in the bag, and I wasn’t going to dispute them since no team — much less a storied franchise such as the Celtics — has coughed up a 3-1 lead in the Finals. But they were talking about next year’s Finals already as if a rematch between the Celtics and the Lakers was preordained.

Every basketball fan should be able to see the appealing logic of the Celtics faithful here. In the 1960s, these teams met six times in eight seasons. In the 1980s, they squared off three times in four seasons. All the talk of a rivalry renewed does seem to point toward another series of Finals matchups between Los Angeles and Boston.

All of that talk, though, is just hype, building this season’s Finals into something much larger than, say, last year’s tepid Finals between Cleveland and San Antonio. In reality, I think it’s Lakers fans that can count on a trip back to the Finals. For Celtics fans, the road back to this point is much, much rougher.

Age is the culprit: The Lakers are a much younger team than the Celtics. The Lakers’ rotation is full of players on the upward arcs of their careers. Guards Jordan Farmar and Sasha Vujacic are 21 and 24, respectively. Forward Trevor Ariza is 22. All figure to improve next season. The Lakers’ nucleus is still very much in its prime. Kobe Bryant turns 30 in the off-season. Forward Lamar Odom is 28 and center and power forward Pau Gasol doesn’t turn 28 until next month. In addition, no conversation about the future of the Lakers is complete without mention of Andrew Bynum: The third-year pivotman was in the midst of a breakout season averaging a double-double and shooting 64% from the field when injuries prematurely ended his campaign. He’ll be back next season, and will celebrate his 21st birthday just before opening night.

The only Lakers starter who figures to decline next season is point guard Derek Fisher, and he might be pushed to the bench by Farmar’s surprisingly solid play. Lakers coach Phil Jackson was never any good at developing young players when he was on the Chicago bench or in his first stint with the Lakers, but this season, Big Chief Triangle has added a new skill. Thanks to their coach’s savvy handling of their young players and the fact that their nucleus is still in its prime, the Lakers figure to be the team to beat in the West until Portland or New Orleans matures.

Despite the giddy optimism of my pals this weekend, the forecast for the Celtics is much less rosy. Basketball players begin to decline after their 30th birthday, which doesn’t bode well for the Celtics roster. Their nucleus consists of forward Kevin Garnett, 32, swingman Paul Pierce, who turns 31 in October, and guard Ray Allen, who turns 33 over the summer. All three of these players are declining from remarkable heights, but each is unlikely to match his current production next season. Two of the Celtics’ key role players — guard Sam Cassell and forward P.J. Brown — are likely to retire rather than play another full season; both are 38. Another key reserve, swingman James Posey, is 31.

The Celtics do have several talented young players on their team. Starting point guard Rajon Rondo is only 22 and his off-season agenda couldn’t be more obvious: He must develop an outside shot. His inability to make an open jumper (he’s shooting 36.4% from the field) has enabled the Lakers to play defense five-on-four whenever Rondo is in the game. Also, Rondo’s own confidence is shot. During Game 5, he beat two defenders to the rim — then passed on the layup.

“They have Bynum, but you haven’t seen Big Baby,” shouted one of my friends, and I realized at that point that the booze was not only doing the talking, it was doing the thinking, too. Rookie forward Glen “Big Baby” Davis was as interesting as any first-year player could be. He slipped to the second round of the draft due to concerns about how his 289-pound frame would hold up in the NBA. Not very well is the answer so far. Before the break, Davis stood an outside chance at Rookie of the Year. Per 36 minutes, he was nearly averaging a double-double and shooting 53% from the field. Sometime during the All-Star break, though, he hit a wall and never recovered. His shooting percentage nose-dived to an unacceptable 43.1%, and all other phases of his game — turnovers, rebounding and even free-throw percentage — declined markedly.

Center Kendrick Perkins is only 24, but he’s been around for awhile. After 288 games over five seasons, he is what he is — a solid role player. He’s not a superstar in waiting. I like Leon Powe, 24, but as long as Rivers insists on playing him like a deep reserve, it’s hard to know how much he will contribute next season.

Adding to the Celtics’ rough road to the 2009 Finals are the opponents. Cleveland and Orlando figure to be better. Philadelphia could be much, much better, and old rival Detroit may not decline that much.

The Celtics are an easy team to figure out: They have an aging core of players, two key players likely to hang it up, and only two young players, Rondo and Powe, who are likely to improve dramatically. Almost every team that has reached the 66-win-or-higher plateau has declined markedly the following year. Although Lakers fans can expect basketball in June for the next few years, the Celtics are more likely to decline than they are to reach this peak again.

mjohnson@nysun.com