Something I do with school students - albeit usually ones way below year 13 - is get them to discuss the following things about what they want from their future career but ban them from mentioning any actual jobs. The ones I talk to are all interested in either healthcare or medical science; the point I'm trying to get them to is deciding which of those two pathways they're more interested in.
what kind of environment/setting do I want to work in?
what kind of environment/setting do I not want to work in?
what kind of people do I want to work with?
what kind of people do I not want to work with?
(these questions cover both colleagues and clients, if appropriate)
do I want to work regular hours?
do I want to know in advance exactly what I'm going to be doing each day?
what do I want to be able to achieve?
what do I want to be able to contribute?
This helps some people identify things they definitely aren't interested in and sometimes suggests things they hadn't previously thought about that they would be interested in.
This is only a preliminary step, of course, but unless someone wants to be an academic it's not necessarily a good idea to just go to university to continue studying a subject they've done at school without thinking about what happens after that. If someone defines what they want to do and it's something that requires a good degree without any conditions on what that degree is in then, yes, it's fine to carry on with something you enjoyed at school. I would still challenge (very vigorously) someone who wanted to do this, as I think they should look at all the courses that are available at university and aren't available at school before they make a choice.