I‘ve never seen adult apprentices, don’t think it exists. Rather you‘d do internships and evening schools, as everywhere else. The difference mainly comes from apprenticeships being the norm for teenagers, it creates IMO an environment of comparatively high skill levels in all kinds of trades. Maybe not too surprising that Germany and Switzerland are generally good at machines and fine mechanics.
20ish sounds about right - in Switzerland, men loose a year due to military/civil service.
We had someone doing an internship in our SWE company (Switzerland) whom I estimated about 60 years. But never heard of someone doing an apprenticeship beyond late twenties or so (may exist, though).
To be honest, I find the idea of classifying people from journeyman to master rather unsuitable for today's knowledge work. It does not pass the smell-test for gate-keeping.
What you need to know changes every five years. Call someone grand-master of software engineering, sure, but no matter how great they are they'll not get your CRUD database UI done any faster - if their career was all about signal processing for particle accelerators and medical device certification. More likely, they'll over-engineer and over-spec and not be prepared for requirements to change completely after a year, or for sinking several days into CSS layout issues. Beyond a certain baseline of experience (say, working five years in the field or so), what counts is knowing the domain well (interpreting what the customer wants). Or already having experience with the technology that applies to problem-of-the-day. Or being highly motivated to learn it.
It's not like crafting with wood. The nature of wood doesn't change every six months. The tools we use to work wood don't change every six months.
20ish sounds about right - in Switzerland, men loose a year due to military/civil service.