Moderator
James Huff
(@macmanx)
Volunteer Moderator
We don’t really track the original install date, probably the closest would be the date of the first published post or page.
You can see version number at the bottom of the Dashboard.
Unless you have a backup to restore from, we do not recommend downgrading.
Also check the Uploads folders. It could be (but not guaranteed) that the site uses the date structure in the uploads dir. Then you can see the minimal month and year.
WordPress stores every user’s registration date in the wp_users table, which for the first user, will be the exact date and time WordPress was installed.