Sorry for such a late reply but it seems u would have just started year 10 so not too late. First and foremost, the young scholars program is not as specials as it seems. I am currently involved and the biggest advantage is access to there library, chances to network and meet some uni students/professors if u r uncertain and it makes you stand out as an individual among a cohort. That is all nice however it is a fairly vain project that seems to be more aimed at identifying students who take initiative and watch for ATAR results. As to how to get in, honestly do not stress it was fairly easy for me, I will give u the run down.
1) Your school gives you permission to apply, sometimes u need to apply for it if many try to go for it.
they r allowed to select 5 students to apply and r required to rank them and give reasons why they were chosen/who is best etc. This is done at there discretion and sent ONLY to UOM.
UOM then look at your scores but personally they also look at ur co curriculars. It says on the website u should be in top 5 or 15% or something, however whilst I was easily top 25%, cause I was taking some of the more harder classes I was not top 5%. Luckily I had participated in pretty much all co curriculars like chess, debating, volunteer work, open days, music, math and science coemptions like TOM and AMC etc. I was also SRC in year 10 so i guess that could be good. My grades also were still very high so even if your grades aren't top 5%, u can make up for this with co curricular activities. Conversely, perhaps having high enough grades would offset if you don't do any co curriculars but i doubt it as they ask about it on application.
So my advice summed up: Don't stress too much it is not that important, definitely pick up some co curriculars, maybe volunteer for open days or something and make sure ur grades r good. Also work hard on application don't rush it on day it was due like me. But based on ur description i'm sure u will get in, but keep in mind that even if only 1 or 2 kids apply for it per school, each of those kids all take accelerated classes so stand out by showing ur character outside of class!