You can find out the date by following the steps here: https://goo.gl/DUzHk
Direct link:
https://www.google.com/dashboard/migration/?srcAccount=USERIDHERE%40gmail.com&hl=en_USMine was created on: May 10, 2004
Direct link:
https://www.google.com/dashboard/migration/?srcAccount=USERIDHERE%40gmail.com&hl=en_USMine was created on: May 10, 2004