If you don't have the OTP codes and didn't set up a backup, and can't access any computer/device where you have access from logging in during the past 30 days:
3) You'll need to fill out an account recovery form to verify ownership of the account. Take time to answer each question to the best of your ability. The form was designed to ensure that no one can gain access to your account except you. Since Google doesn't collect a lot of information about you when you sign up for an account, we will ask you questions like when you created your account, what Google services you use, and who you email frequently (if you use Gmail) to make certain you are authorized to access your account.
I've been called on a few occasions to recover the gmail accounts of family and friends and it hasn't worked once, even when supplying reasonably accurate data.
Same here; that's why I forwarded the oldest email in my account to another address, took note of the date on it, and saved it to my hard drive; headers intact.
Keep in mind each fallback/recovery option like secret question, secondary email address, OTPs etc. is an extra attack vector too. So would be good idea to store that old email somewhere securely too...
If you don't have the OTP codes and didn't set up a backup, and can't access any computer/device where you have access from logging in during the past 30 days:
3) You'll need to fill out an account recovery form to verify ownership of the account. Take time to answer each question to the best of your ability. The form was designed to ensure that no one can gain access to your account except you. Since Google doesn't collect a lot of information about you when you sign up for an account, we will ask you questions like when you created your account, what Google services you use, and who you email frequently (if you use Gmail) to make certain you are authorized to access your account.