If by old you mean the createdBefore field, I think that’s normal. It takes some time create the bloom filters for all nodes, so there is some delay. I think they bake in some buffer time too.
How long the garbage collection process takes does depend on the number of pieces to move, but it is dominated by how many pieces your node has. It has to check every piece, compare the date if it should be considered (createdBefore), and if it belongs in the bloom filter. If it doesn’t belong, then it moves it to trash.