@reluctantbrit I come from the Dutch system which is quite similar to the German system and is also academically selective at 11. When I was at secondary (I am 55) there were quite a few people who had streamed their way through the system after being placed in the GCSE-equivalent stream and so did the equivalent of A levels aged 21. That wasn't anything unusual. It's rarer now. The way subject choice is done has also changed. These days you pick a 'stream' (arts/creative, maths/science, Humanities, languages) and then within that you build your subject choices, but it isn't a completely free choice the way it was in my day.
I did a mixed set of 8 subjects at A level, failed Maths (but that was my 8th) and whether you passed or failed the exam year hinged on the distribution of your grades - you could borderline fail 2 subjects or fully fail 1 and still pass. I did 4 languages, Biology, Chemistry, Geography and Maths. I don't know how Dutch maths compares, but the language requirements were far, far higher than what is demanded at A level for MFL. For French, for example, we had to read a total of 15 books over 2 years, 3 of which had to be plays, 1 a volume of poetry, 1 from before 1800 and a further two dating from before 1900. German and English broadly similar, Dutch (obviously) more demanding still.