This is definitely an option, since your ATAR result is valid for 2 years. So if you have a high ATAR (i.e. 99.0+), and you’re really set on medicine or dentistry, it might be worth taking a gap year to focus on UCAT preparation so that you can apply as a high-school leaver with a high ATAR and a high UCAT score.
Once you’ve started university, the number of available spots in medicine and dentistry decreases drastically, as you’ll be applying via an undergraduate or postgraduate pathway. (We talk more about pathways in this article.)
If you do decide to take a gap year, you’ll also have lots of opportunities to do interesting things, like doing voluntary work that requires you to be 18+ years old (which you might not have been old enough for during high school) or getting a job.