determining avg cache lifetime

[Rihad <admin@xxxxxxxxx>]

Hi, is there a way to determine the average time that a cached item 
lives in the cache ("cache motion", as djb would refer to it)? IIRC 
there was such a thing in cachemgr's output in the older versions of 
Squid: under the "Store directory stats" the value was displayed as 
e.g., "3 days", but lately there's been no such thing in place.

Thank you.