I installed pokemon go on my phone for my son. It's logged in with my Gmail account. I have now bought my son his own phone. Is there a way to log into the game using my Gmail account without all my emails etc. showing on his phone? I never set up a separate username account and have only ever logged in using Gmail. He obviously doesn't want to start at the beginning again.
Your e-mails should not show up on his phone if you log in to the game with your account. Pokemon GO only uses your basic profile info and e-mail address.
For example, my iPhone currently has two different Google accounts logged in to Ingress and Pokemon GO, and the mail app is connected to a third Google account. Android should be no different.
But if you still have doubts, you could always go the new account route.