There's no age limit on VCE. You could ask your current school, ask other schools, or consider an adult education centre.
I definitely think this is something you should tell your parents about, or at least a teacher or counsellor at school you trust. Telling your parents may help them too; they probably know there's something upsetting you that you're not telling them, and it might bring them some relief to know what it is exactly.
I usually strongly recommend against repeating VCE though... Usually the better option is to start fresh at uni or tafe. Even if your ATAR isn't high enough to get into your desired course, you can at least spend some time learning things you're personally interested in, and you can always transfer after a semester or year.
I know exams are soon so you're probably the most stressed you've ever been in your life right now, but believe me when I say it'll pass soon enough. You can do no better than your best, but if you give it your best you've got nothing to regret. If it doesn't work out, there's plenty of Plan Bs available to you, but try not to worry about that unless the time comes for it
