Yeah, i dont think its a good idea to decided what you want to do early on.
I really believe that building the foundations are important and primary schools and lower secondary education should really focus and drill in hard on the fundamentals. There are kids in my sisters Year 4 grade who still know none of their timestables or understand them while the teachers carry on with drawing and painting. This will put you behind and theres the potential to be perpetually behind (maybe a big of an exaggeration but you see my fundamentals point right).
I think it would be good to offer a watered down version of Yr 11/ Yr 12 in the proceeding years sort of as a sampler and tell them thats what VCE will be like. I remember year 9/10 SOSE/ Humanities we were doing history and torts (law) and all that. I didnt realise that this kind of corresponded to VCE History and VCE Legals. If i had a chance to sample a little bit of all the VCE subjects i believe i would of made some different choices, you go in kind of blind based on a couple sentences of descriptions (well i did).
For example chemistry below year 11-12 was nothing like it is now, i honestly thought itd be like that but boy i was wrong ( i needed chem anyway, well i did at the time and changed career choices but i still need it so its all good).
Another example, biology, pre Yr 11-12 biology was pretty different as well. I didnt think i liked biology very much or would like it at all. I had 5 subjects on my subject selection sheet in year 10... i needed one more... so i just decided to fill it with whatever my mates were doing... it was a toss up between biology or geography... im lucky i chose biology.. i absolutely love the subject and i wouldnt of known this if i never made that random choice. Im lucky in that respect because the geography students get royally screwed over.