USYD's website states that mature-age entry students are only eligible for a select set of courses: https://www.sydney.edu.au/study/applying/admission-pathways/...

Being fair, they do make it sound as though you can enter a degree you're eligible for, and then apply to transfer to another degree after a year of study. If you're transferring to a similar degree, your completed course units would probably count towards your total required elective units.