Gmail account won't connect on early 2015 MacBook Pro

Update: It took a while, but Mojave is now running on my son's laptop (the early 2015 MacBook Pro). In order to install Mojave, he had to first install High Sierra, followed by a High Sierra update that crashed a few times during download. I clicked "More" in that update in the App Store, and saw that it was two updates bundled: an OS update and a security patch. I successfully dl'd the update alone, and then tried the security patch...which crashed. So, I took a chance on trying Mojave without the High Sierra security patch, and it worked.

Due to the crashes, I did uninstall Bitdefender completely from his laptop, and turned off his parental controls on my laptop, before installing Mojave. I had hoped to address one variable at a time and hold off on deleting Bitdefender. but at this point, I was getting impatient, so I uninstalled it before dl'ing Mojave.

The college gmail account then installed with his new account PW, and is working fine.

I am using OpenDNS to block his most common daylight time wasters, but it doesn't give device-specific controls like Bitdefender does. I will probably try to reinstall Bitdefender in a couple of days, and see how it goes. I will give you an update after that.

Thank you again, Eric! You're Level 10 status is deserved. :-)

Update:

I reinstalled Bitdefender with parental controls on son’s laptop, after finishing Mojave and fixing his college gmail account. After 2 weeks, everything seems fine on all fronts. The problem seems to

have been my son ignoring numerous OS upgrade notices. 😬

Thank you! I will get to work on that, and report back.

I did first check his OS version for updates, and was mystified as to why his early 2015 MacBook Pro wouldn't show any macOS update beyond Sierra, while my mid 2015 MacBook Pro is running Mojave. Like most teens, he is quite adept at ignoring non-automatic update notices...

So I will start with Mojave and see what happens. I did look for that first, but as you indicated, it isn't obvious how to do it now that he has missed the initial launch install window.

I am using Bitdefender for multiple reasons, after researching my options. One of them is parental controls of devices (although the troublesome email is a college account, my son is a teen at home using dual enrollment). I turned off Bitdefender on his device, and on mine (parental controls), but I did not completely uninstall it. No similar problems in the rest of the house, including two iPads, three laptops and three iPhones. Just this one account on this one laptop.