Gmail not working

Google removed Exchange support for all but paid uses in January of last year. It did however grandfather in existing users on their existing devices. If you were using gmail in this way on your old device, it will not work using the new iPad Air.

Delete the account on your new iPad and simply create it again. It should work fine.

If it's still not working, perhaps reset your gmail password on your iPad, that's the easiest solution I think, hope this helps.