They were slow paced because Rondo wasn't a threat offensively, not because the big three were old. KG, Pierce, Allen during that period after the ship would have no problem playing with a pg they played at a faster pace.
they couldve played faster, yea prob..but doc was big on minutes to make sure they were rested..they also just wanted to get into the "Dance" healthy and rested rather than scrap random games since they were confident they could beat anyone in the playoffs
first time around they had posey/pj brown/perk etc that wasnt conducive to a fast paced team either
they also were generally the most experienced team in the league...they wanted to take their chances strategically rather than let the other team get easy transition buckets. they were much better half court defensively as well..
rondo's stats were helped by having 3 HOFs on his team yea, but they also needed a PG like him to set up these guys whose abilities to create their own shot had diminished. theres a reason why lebron and kobe switched onto him in the playoffs..