I'm just a fellow flight simmer in the UK, but I suspect that the 'out of date' message refers to the navigation data held in your X-Plane folders. This data is based on something called the AIRAC cycle published every month by the International Civil Aviation Organisation. The data is used by the whole aviation industry and flight simmers alike.
Because new AIRAC data is published every month, the information held by all X-Plane simmers (and others) will more or less always be out of date. Basically then, long story short, you can ignore this message, it won't affect your flying experience!
As far as terrain is concerned, please confirm the navigation system you are referring to i.e. Garmin G530, G1000 or other?