Google only allows email changes if you didn't create it with a gmail address. When I found this out years ago I immediately scrapped that account and created a new one with a non gmail address before there was too much on the original account.
That might be technically true, but in practice not an issue. I have a Gmail account, so the primary address is fixed because the address is the account, however I use a different address to sign-in, and Google recognises those addresses as being on that account. For pretty much all uses my account has a different email address.
