HMarie I had the same problem as you with my old IPad (^refusing to do anything unless I key in an Apple ID for a long-defunct email address^), the reason is that you cannot yourself change the primary email address through your Apple account!! Presumably their software was written before people regularly changed their email addresses?
Anyway, one day I decided to phone the Apple helpdesk. At first the helpdesk person said nothing could be done so I launched into a harangue - Apple are one of the biggest corporations in the world and you can't allow me to make a simple change, I've been using Apple computers since the year dot, still have an original IPad...and so on whereupon she consulted her manager and they put me through to someone in the US (their cost) who spent a long time trying to understand my problem and when she finally got it, she made the changes online and changed my primary email so now, hurrah, I have an up to date Apple ID! How bizarre that they haven't allowed this simple change by the user, must be millions with the same problem.
With regard to the OP, I've been a computer user since the very earliest days and used to have some technical skill and was trained in numerous programs on both Apple Macs and Windows computers. I now think that our computer-run world has become absurdly complicated for the ordinary user from how to store data, to online bookings, virus protection, software installation and updates and myriad matters. I loathe Windows 10, my computer recently spent 2 hours installing the latest updates, was unusable in that time and had, again, I realised reset some of my defaults. Bl**dy Microsoft, if a car manufacturer sold a car that was undriveable for hours at a time while it took itself off to a garage to be serviced, they would go out of business but we are now all in hock to this massive corporation!