It refers to a person who is unemployed, not receiving an education or in vocational training. I'm not sure if the acronym is commonly-used in your country, but if it is, then do you use it to describe someone who are in their late 30s, 40s and 50s also?
In British English we normally refer to being in the various stages of education this way: I'm at school ('in' is more American) I'm in college ('at' is common too, though) I'm on a course (either a college course or any other kind of study, such as a vocational study or a training programme) I'm at university
It would be understood, and sounds natural, but the -al is not necessary; "vacation" is a perfectly good adjective. And, ate to brake this too you, but even people running shools sometime make usage airs. By the way, I believe your example about the "vacational college" was a typo or brainfart for "vocational". As for your example in comment above, I certainly wouldn't follow the usage example ...
Is this the right way to write about choices limitation. Students' choices should be restricted\limited to\in vocational courses. Or Your choices are limited to\in the following options (a or...