playing and age are two different things.
as far as age, around 10 years I noticed my shen plywood really started to sound like it has been played in. for a plywood/not that old bass, it really does sound mature. I have had a shen dealer/luthier comment on how nicely it has aged. the label reads 2006.
as far as playing? Gary Karr says just a few hours of the right type of "opening up exercise" gets it going just fine -
I actually agree with the Karr method, playing 3rds, major and minor, all the way up and down the instrument. those vibrations will be more than enough to get the instrument ready to vibrate. Just don't do it where anyone can hear, cause if this is done properly most of it is really annoying.