Kevin Garnett turns 35 next week. Pierce will be 34 in October. Ray Allen turns 36 in July. Each star occasionally still shows flashes of greatness. But they no longer seem capable of playing at a consistently elite level through a seven-game series — at least not against a younger, equally talented and more athletic opponent.

It is hard to imagine the Celtics getting any better without an infusion of young talent. That will be difficult. Boston has $65.8 million in committed salaries for next season, not counting a potential new contract for Green, who will be a restricted free agent. Two of their younger rotation players, Davis and Delonte West, will also be free agents. Jermaine O’Neal (who turns 33 in October) remains on the books, and Shaquille O’Neal (39) has a $1.4 million option to return.

The Celtics will not have salary-cap room until 2012, when the contracts of Garnett ($21.2 million) and Allen ($10 million) expire.

The Celtics’ championship window, which once seemed so wide, has been reduced to a razor-thin beam of fading light.