Do you think a restaurant run by teenagers would be successful? You don’t have to speculate. McDonald’s is run almost entirely by teenagers, as is every other fast food outlet in Australia. My daughter is one of those people who work in a customer facing role.
The options available to you before the ATAR assessment process is completed and after are different. If you are in a situation where your ATAR does not get you into your preferred course, there are still several options open to you. Remember it is not where you start but where you finish that is important.