Nginx proxy cache doesn't update cache-control max-age time!

[J.R.]

> There is no Age header support in nginx as of now (relevant ticket
> in Trac: https://trac.nginx.org/nginx/ticket/146).  If you want
> pages to expire at a specific time regardless of intermediate
> caching, consider using the "Expires" header.

The 'age' header appears to be something else... What I'm talking
about specifically is part of the 'cache-control' header...

For example:  "cache-control: max-age=9848, public, must-revalidate"

Without max-age decrementing while in the nginx proxy cache, all
client will receive the same cached number until the cache is
refreshed.

Since the proxy cache is storing the cache time internally (so it
knows when a page expires from its cache), one would think there could
be some way to get the max-age value to be updated from that internal
data.