My game says it's out of date, even though gog keeps it up to date. Was a patch not released on gog?
Please try reinstalling the game and deleting all local files under C:\Program Files(x86)\GOG Galaxy\Games\Hrough the Ages\
This should help with the issue. Let me know if there are any further troubles.
(Don't forget to sync your profile to your online account or back up profile data to prevent its loss.)