You can create a Google account using a non-Gmail address, then create a YouTube account using that Google account. I just tested this with a Fastmail alias, and it works fine.
- Start here:
https://accounts.google.com/signup/v...gnUp&nogm=true
- Create a Google account with a non-Gmail email address on that page. You will need to receive an activation email sent to that new email address.
- Sign in to YouTube using the email address you used for the Google account.
Bill