I too am in year 11 and wish to pursue IB. Just for a disclaimer though as I am neither a current IB nor a graduate I can't give you any certain advice. However, as I've been looking into it I can regurgitate some info back to you.
There are no definite pathways to enter IB however the combination of courses and unis to get in can be organised in a matrix. Group of 8/sandstone unis are the most desirable with USyd and UMelb being clear targets. Some combination of commerce in a double degree is favourable but comm/law (for some reason) is the most sought after by IB recruiters. Overall, the matrix would go something like this: (correct me if I'm wrong BTW)
| God tier unis
Usyd
Umelb | Target unis
UNSW
Monash
ANU
UQueensland | Semi-target
UTS
Maq
UWA
UAdelaide
UTasmania | Non-target
Newcastle
Wollongong
WSU
Some others that aren't in sydney |
God tier courses
Law/comm | Jordan Belfort | Target | Semi-target | Non-target |
Target courses
Comm and Computing/Actuary/Math/something quantitative
Doing an honours year is also favoured for whatever you do | Target | Semi-target | Non-target | |
Other comm double degree | Semi-target | Non-target | | |
Straight comm | Non-target | | | |
Non comm | | | | |
The ATAR range for Comm/law at Usyd or Umelb is around 99.5. I don't think I'll even get that.
The ATAR for something like UNSW or ANU Comm/law is around 97 which is what I'm aiming for atm. (Beware for UNSW comm/law you'll have to sit the LAT)
For Comm/quantitative major it can vary from high 99's to low 90's. For these, it's best to do your course to a high standard (High distinction + honours if possible) to set yourself apart.
Whatever you do, ensure you're doing some decent extra-curriculars like finance society or investing society or something like that. It's best to be on the leadership team for these. In your interview you'll have to make up some story about being passionate about finance at a young age or some BS. EC's provide at least evidence that you do genuinely want to go into IB and are not there for the money.
This post on WallStreetOasis has some good advice:
https://www.wallstreetoasis.com/forum/investment-banking/qa-australian-ib-life-etc