Everyone has given you really good advice! If your just starting high school theres nothing to say you wont get the grades to become a vet!
My step father knows one of the top equine vets in Australia, and he's always saying theres a shortage of vets specialising in horses, apparently they all want to do small animal work. So theres definitely places available and it pays well!
I don't have much to add, I just thought id give a list of UNIs/colleges that I know of in case you wanted to go down that road, and careers as well. It can't hurt knowing this stuff lol
UNIs/Colleges that offer equine science/management: (these all have websites btw)
Charles sturt uni
Uni of queensland
Theres also a bunch of tafe courses, but I know a few people who have done them and I don't think theres much point in doing it.
And of course, theres Unis that offer vet science, especially sydney ones but I didnt include those because I don't know much about it.
As for getting into UNI, they usually start giving you info around yr 9/10, We have ATARs in NSW (used to be UAI) and QLD have OPs. Both are different but can be converted to give students an idea of how they have to go to get into a uni from a different state. If you don't get straight in, based on your OP, there are always many different pathways into uni, they vary depending on the particular one though. But at this stage you don't need to worry about this so much. Just getting through what your doing now.
Anyways, careers: (theres SO many of these, so just a few)
Stable manager (and all other positions below this)