Yeah, let's pick the method that will lead to the conclusion that we want, your internships at higher courts have taught you well
Surely, the minimum of rule of law is that if X is okay for A, it is also okay for B, even though B is not /ourguys/. It may disproportionately affect the higher court judges, but the table linked is specifically about higher courts and it seems all good for Germany, Finland or the Dutch to kick out geezers from their Supreme/Constitutional Courts.
If the rationale for such provisions is that after a certain age, a judge is highly unlikely to be mentally fresh enough to do the important job of a judge. It seems obvious to me, that if you are not fresh enough to deal with unpaid invoices and public intoxication on the district level, then you are definitely not fresh enough to deal with the complex cases at higher or even the highest court. Otherwise it just gets embarrassing like the Zuckerberg hearing where the boomer senators where wondering omg how Facebook could possibly make money if it doesn't charge the users anything and they needed the CEO to have the novel and arcane concept of advertising explained to them.
Why shouldn't it affect the sitting judges? On the contrary, it would be arbitrary if it
didn't apply to them. Again, the rationale of not being sharp enough to do the job, has nothing to do with when you were appointed. If "the people" determined that you are too old, then you are too old. The office of a (supreme court) judge is not a family heirloom shotgun or a veteran car that could be benevolently allowed to be grandfathered in.
The extension at the discretion of the President is ****ty and they should get rid of it. That's the only problem I'm seeing in the whole case, although I'm still far from sure if it's big enough a deal to warrant triggering Art 7 or cutting funding.
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Besides, the general level of judicial entitlement is ridiculous. It's kind of impressive tbh how they managed to navigate through the 19th and 20th century as the only group that convinced everyone else that it is not only ok, but even desirable to be appointed for life. Yeah for everyone else, power corrupts and having someone in charge indefinitely is superbad, but you can totally trust us. Checks and balances for everyone. Everyone else. Checking the judiciary in any way whatsoever? What are you, a populist?!?