I am unable to access Gmail on my iPad Air 12.5.7

Google has strengthened its security and older operating systems are no longer directly compatible.

To connect your Gmail account on your iPad:

1. First of all, delete the Gmail account.
2. Then, you will have to create an application password: Google - Application Password.
3. Finally, when you add the Gmail account in Mail on your iPad, choose "Other" and not "Google". Fill in your email address and application password.

You need to have 2-factor authentication activated on your Google account to be able to generate app passwords. If you do and have trouble accessing the link above, try this direct link instead: https://myaccount.google.com/apppasswords.