i'd have to say your conjecture about access and ages isn't accurate. i had as much trouble as anyone else, i started my sims3 account in 2010 and it's been active since then, and am definitely way outside the age range that the media ban is targeting
This is not the case about older accounts and older simmers, my friend she_devil cannot get on at all yet and her account is old. One of mine that I still CANNOT sign into is old. Just because I have logged in on this account does not mean that I am not also having other problems on this account as I cannot view ''All Activity' for one, I get the 504 error if I try. This is a 2009 account and I could not log in on numerous occasions weeks ago. The person who started the thread liesemietze has only just got on the site after two months and that is a 2009 account. So no that is not the case that the older accounts are not having problems. Kb777 has only just managed to get back on and that is an old account. The old accounts have had just as many issues as the not so old accounts... I don't think anyone can change their privacy settings, there is an error with that too. Many are stuck in the same settings and cannot change them. I also don't have share to Facebook any longer.
It seems to be coinciding with the launch of the new law of the social media ban for under 16's in Australia, which officially started yesterday, and for which other sites, like Meta, have been implementing things for a couple of weeks already. The Sims 3 website has a link to-sign into-share on Facebook feature, which is also in the game so I don't know how it would effect that, just be an empty button I suppose. You might find that there are interruptions on the Sims Discord thing as well.
People not having any trouble are probably ... not as young. Somewhat older.
Here are the social media links down the bottom of the page
And the share-to-Facebook buttons in the studio memories that used to be there ... are gone now.
This used to have a Facebook icon for sharing each memory in my studio
Clicking on the links down the bottom of the page under 'Stay in the Loop' these days takes you to either The Sims official You Tube Channel, now banned to under 16s in Australia, and to the Sims official Facebook page, also banned to under 16s in Australia now. Twitter, now X I don't have and its reported on the news its not clear what's happening with it.
My guess is the maintenance has been about that, and the long time active accounts obviously older are probably the one's not having problems