What does the keypoololdest field mean?
The value 1392447127 is exactly Sat, 15 Feb 2014 06:52:07 GMT in  Unix timestamp 
check it here : http://www.onlineconversion.com/unix_time.htm

keypoololdest gives the unix timestamp of the oldest key in the key pool (which stores unused keys). This timestamp can be used to check if a wallet backup still covers all your used keys or a new one needs to be created.

At the latest, if the timestamp retrieved with keypoololdest gives a date younger than your youngest backup, you should create a new backup.