[Debian 7] Storage age about 10-15% more for high priority bucket only as opposed to low priority bucket only.

Steps to reproduce:
1)Create a low priority bucket and insert 100k items.
2)get the storage age statistics.
3)delete the low priority bucket and create a high priority bucket. insert 100k items.
4)get the storage age statistics.
5)upon repeating this test, it is consistently seen that storage age in case of high priority bucket only is 10-15% higher than low priority bucket.