The Gmail account creation date will help you recover or reset your Gmail password and your Gmail username account. If you have forgotten it, please refer to this article.
How to know the date of Gmail account creation
When you sign up for a Gmail account, there are 3 Google welcome mails, you check the time of that email to know the Gmail creation date.
If you deleted the 3 mails, see way 2 below.
Step 1: Open your web browser and access to Gmail Sign in page
Step 2: Click on the gear ⚙ icon on the top right corner of the screen and select “Settings”.
Step 3: Click on Forwarding and POP / IMAP in the menu.
Date in POP Download Status is the date you create Gmail account. Good luck!