Oops I see. You meant the actual address - johndoe123@gmail…..I think he's referring to the actual email address. You can change your name in gmail settings but that won't change your email address.
It's one reason I got my email address back in 2004, was able to get the name I wanted as they all hadn't been taken up yet. Only drawback is that you get a lot of spam and also people with similar names to you end up sending you mail.