Instead of scrapping the Main_Page page, we could use this MediaWiki endpoint:
/api.php?action=query&prop=info&titles=Main%20Page&inprop=created
For instance: https://gardening.wikia.com/api.php?action=query&prop=info&titles=Main%20Page&inprop=created
Which retrieves the date of creation for the page called "Main Page".
This also would help for retrieving the date of creation of wikis using no-Gregorian calendars.