Here is a simple trick to find out your Gmail account creation date.If you have deleted the first email sent by the Gmail team then there is another yet neglected method to find it If you have not changed your POP settings
Go to Settings –> Forwarding and POP/IMAP from your gmail account.
Now search for the line:
1. Status: POP is enabled for all mail that has arrived since YOUR DATE
You have your account creation date
Note:
This date is very important is security aspects! So don’t share it with anyone
Credits: Swashata
it will be better if you enabled the "Enable POP for all mail" and then check it. Since some body may setit as "Enable POP for mail that arrives from now on" then it will show the date when he set the pop settings.