If its mostly bark I would not worry about it being composted/aged or not. Problem with bigger than ideal peices is that the young plant will grow into it fine but when it gets big enough and the water demand increases if you dont stay on top of the watering and keep those large peices of bark wet enough your plant will go south fast. You can sift it with 1/4" or 1/8" wire mesh, but its a little bit of work.
Damon
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