Original Beschreibung (engl.):
The Age response-header field conveys the sender's estimate of the
amount of time since the response (or its revalidation) was
generated at the origin server. A cached response is "fresh" if
its age does not exceed its freshness lifetime. Age values are
calculated as specified in section 13.2.3.
Age = "Age" ":" age-value
age-value = delta-seconds
Age values are non-negative decimal integers, representing time in
If a cache receives a value larger than the largest positive
integer it can represent, or if any of its age calculations
overflows, it MUST transmit an Age header with a value of
2147483648 (2^31). An HTTP/1.1 server that includes a cache MUST
include an Age header field in every response generated from its
own cache. Caches SHOULD use an arithmetic type of at least 31
bits of range.